Shortcuts: Steam menu, commands, and modifier taps

Key combinations (and mouse and controller buttons) get two new actions:
- steam_menu: Open Steam menu / close dashboard (steam/ft-steam menu).
- command:CMD: run CMD with sh -c, as the relay's service, with layout/,
  float/ and steam/ on its PATH. Input Settings offers it for key
  combinations as Run a command...
Both work without pointer mode.

A modifier on its own is now a key combination too: a tap, pressed and
released with no other key, mouse button, or scroll in between. A bound
tap sends the desktop F24 before the release, so Plasma's launcher stays
shut. The defaults gain a Meta tap for the Steam menu; this replaces
META_DASHBOARD, which only worked in pointer mode.

input/test/keys-test.py runs the relay against fake devices with every
outgoing socket renamed, so it's safe next to the live relay.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/reference.md

@@ -85,6 +85,8 @@ The relay also owns the volume keys, on every device that has them, the headset'
 desktops.sh relay install     # enable it (starts with the next reboot or SteamVR start)
 desktops.sh relay status | log | uninstall
 input/input-relay.py --no-grab   # try it without taking devices from SteamVR
+input/test/keys-test.py          # key combinations and modifier taps, against fake devices (safe next to the live relay)
+steam/ft-steam menu              # what Open Steam menu does; ft-steam check: Steam's UI still has the calls
 ```
 
 The first time, the relay has to start before SteamVR, so reboot or restart SteamVR after installing it. After that it's safe to restart on its own: systemd keeps the virtual devices open in its file descriptor store (`FileDescriptorStorePreserve=yes`), so SteamVR keeps the same devices.
@@ -99,7 +101,7 @@ A mouse drives SteamVR the way a controller's laser does, but shows up as a smal
 
 Whichever device you used last wins. Picking up a controller hands the laser back at once, and moving the mouse takes it again. When the headset comes off, the pointer lets go, so the displays can sleep, and it stays off until you're wearing the headset again.
 
-To move a floating panel, left-drag its grab bar. The scroll wheel pushes and pulls it while you drag. Hold the right button while dragging and move the mouse to tilt the panel around the grab point; the right press isn't sent as a click. The tilt stays for the rest of the drag, and releasing the left button drops the panel as it is. A mapped Toggle dashboard button (or a Meta tap, with `META_DASHBOARD=1`) wakes the pointer if needed and holds the virtual system button for 0.12 s, because SteamVR ignores a press and release in the same instant.
+To move a floating panel, left-drag its grab bar. The scroll wheel pushes and pulls it while you drag. Hold the right button while dragging and move the mouse to tilt the panel around the grab point; the right press isn't sent as a click. The tilt stays for the rest of the drag, and releasing the left button drops the panel as it is. A mapped Toggle dashboard button wakes the pointer if needed and holds the virtual system button for 0.12 s, because SteamVR ignores a press and release in the same instant. Open Steam menu / close dashboard (`steam_menu`) needs no pointer: `steam/ft-steam menu` asks Steam's UI, over its debugging port (`steam/steamui.py`), to show its dashboard overlay and focus the Steam frame's menu, or to hide the dashboard if it's up.
 
 ```
 pointer/driver/build.sh && pointer/driver/install.sh install   # then restart SteamVR
@@ -114,10 +116,10 @@ The pointer settings are in `~/.config/frametop.conf`: `POINTER_SENSITIVITY`, `P
 
 A Kirigami app with a Python backend, in the Plasma menu under Settings. It runs in the `dev` container and talks to the relay over its control socket, `@frametop_relay`. It has eight pages:
 
-- Devices lists every USB and Bluetooth mouse and keyboard, with a light that flashes when the device is used. Each device gets a role: 3D pointer (grabbed, drives the pointer; the default for anything with a mouse), Pass through (grabbed only while typing goes to the desktop; the default for keyboards, where a Meta tap toggles the dashboard if `META_DASHBOARD=1` is in `~/.config/frametop.conf`), or Ignore. A device is identified by its Bluetooth address, or its USB ids and name, so all of its input nodes share one role. Forget drops everything saved for a device.
+- Devices lists every USB and Bluetooth mouse and keyboard, with a light that flashes when the device is used. Each device gets a role: 3D pointer (grabbed, drives the pointer; the default for anything with a mouse), Pass through (grabbed only while typing goes to the desktop; the default for keyboards, whose key combinations work everywhere), or Ignore. A device is identified by its Bluetooth address, or its USB ids and name, so all of its input nodes share one role. Forget drops everything saved for a device.
 - Buttons maps a pointer device's buttons. Choose Capture a button, press the button or key, then pick an action: a click, back, scroll, toggle dashboard, recenter, pointer on or off, head follow on or off, gaze pointer on or off, gaze precision, gaze drag, gaze quick check, faster or slower, reset the screen layout, hide or show the screens, open or close the keyboard, float a window in VR or put it back, put all floating windows back, Open profile NAME (one per profile, [profiles.md](profiles.md)), pass the key through, or nothing. Devices with saved mappings are listed even while they're asleep.
 - Controllers maps the Frame controllers' buttons (every button but the system button) to the same actions, except passing a key through and the gaze actions: gaze mode is a mouse and keyboard feature ([gaze-controllers.md](gaze-controllers.md)). Capture a button and press it on a controller, or pick it from the list. The controllers aren't input devices on the host; only SteamVR sees them. So the pointer helper reads them with SteamVR input (`pointer/helper/vrbuttons.h`, `pointer/helper/actions/`) and sends presses to the relay (`vrbtn right/a 1`), which does the mapped action. The helper only takes the buttons that are mapped (the relay tells it with `vrbind`), at an overlay-global priority, and only while no game (scene application) runs, so games keep every button; with In games on (`controller_in_games`), a mapped button is taken from games too. That needs SteamVR's "Enable global input from overlays (Experimental)" setting (`steamvr/globalActionSetPriority`), which the page's Global input switch turns on and off. Mappings are saved as `controller_buttons` in `~/.config/frametop-input.json`.
-- Keyboard sets when Frametop's keyboard opens: whenever a text field is selected; only while no pass-through keyboard is connected (the default; keyboards other programs make through uinput, like frame-voice's, don't count); only with a mouse or controller button mapped to Open/close keyboard; or never, which turns the button off too. Keep it open (on by default, `vr_keyboard_persist`) leaves it open after the text field loses focus. The mode is saved as `vr_keyboard` in `~/.config/frametop-input.json`, and the page lists the keyboards that count as connected. Its Key combinations section maps modifiers plus a key, on any keyboard, to any action but passing a key through or nothing. The gaze clicks (Gaze left click and Gaze right click) only go on key combinations. The defaults are Meta+J (gaze left click), Meta+K (gaze right click), and Meta+Shift+F (float window in VR or put it back); remove them or add others there. The combination's last key isn't typed, and the modifiers still reach the app. They're saved as `key_bindings` in the same file.
+- Keyboard sets when Frametop's keyboard opens: whenever a text field is selected; only while no pass-through keyboard is connected (the default; keyboards other programs make through uinput, like frame-voice's, don't count); only with a mouse or controller button mapped to Open/close keyboard; or never, which turns the button off too. Keep it open (on by default, `vr_keyboard_persist`) leaves it open after the text field loses focus. The mode is saved as `vr_keyboard` in `~/.config/frametop-input.json`, and the page lists the keyboards that count as connected. Its Key combinations section maps modifiers plus a key, or one modifier tapped on its own, on any keyboard, to any action but passing a key through or nothing, or to Run a command…: a command line the input relay runs with `sh -c` when you press the keys (`command:CMD`). The command runs as the relay's user service, outside the desktop's session, with `layout/`, `float/` and `steam/` on its `PATH` (so `ft-layout use Work` or `ft-float launch org.kde.dolphin` work as they are), and its output goes to the relay's journal. The gaze clicks (Gaze left click and Gaze right click) only go on key combinations. The defaults are a Meta tap (open the Steam menu, or close the dashboard), Meta+J (gaze left click), Meta+K (gaze right click), and Meta+Shift+F (float window in VR or put it back); remove them or add others there. A tap is a press and release with no other key, mouse button, or scroll in between; a bound one sends the desktop F24 before the release, so Plasma's launcher doesn't open on it. The combination's last key isn't typed, and the modifiers still reach the app; while typing goes to Steam rather than the desktop, keyboards aren't grabbed, so Steam or the game sees the keys too. They're saved as `key_bindings` in the same file; a file with its own list, even an empty one, gets no defaults.
 - Pointer has a Head follow switch and sliders for the pointer settings, which apply immediately, and a Recenter button.
 - Ignored panels lists the SteamVR overlays that are showing, grouped by app (the first two parts of the overlay key, such as `sasaken.frame-perf-overlay`), from the pointer helper (`overlays`). Tick a panel, or Ignore the whole app, and the pointer passes through it to what's behind. It's for panels you only look at, like a performance overlay that follows your view. The list is saved as `POINTER_IGNORE` in `~/.config/frametop.conf`: comma-separated overlay keys, where a shell pattern like `vendor.app*` covers a whole app, including panels it opens later. The helper reloads at once. Frametop's own screens aren't listed, and entries for apps that aren't open are listed below, to remove.
 - Gaze has the gaze pointer switch (on now and from now on; a mapped button toggles it until the helper restarts), what the mouse's left button and movement do, the gaze dot, the eye tracker and eye bias, the gaze mode sliders, the gaze service's state (headset, samples per second, how often the tracker is losing each eye, the calibration, the nudges learned), and Quick check, Calibrate, and Check headset fit (each in a panel in the headset), Reload calibration, and Forget nudges. The gaze probe, a development tool, is in the page's overflow menu.