Map the Frame controllers' buttons; make gaze clicks correctable

The Frame controllers aren't input devices on the host, so the pointer
helper reads them with SteamVR input (vrbuttons.h, actions/), one action
set per button, and sends presses to the relay, which does the mapped
action like for a mouse button. Only mapped buttons are taken, at an
overlay-global priority (SteamVR's experimental "Enable global input from
overlays"), and only outside games unless In games is on. Frametop Input
Settings gets a Controllers page to map them.

Gaze mode: a left press while the gaze has the pointer isn't sent at
once. The pointer stops, you drag it onto what you meant with the button
held, and the release clicks there; a press held still for
POINTER_GAZE_HOLD (0.5 s) becomes a real press, for drags. The dot shows
only while the mouse moves it (POINTER_GAZE_SHOW), while a press is held,
and as a pulse per click. Outside games the pointer stays on while gaze
mode is on. ft-gazed takes a third of each lesson's offset instead of all
of it: in the first live test one 6 degree lesson moved everything and put
the next target 7 degrees off. Frametop Input Settings gets a Gaze page.

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

gaze/README.md

@@ -19,8 +19,8 @@ gaze/ft-gazectl on            # the pointer follows your gaze (off: the mouse al
 Gaze as an input method for the whole desktop, without replacing anything of SteamVR's:
 
 - `ft-gazed` (host Python, a user service: `gaze/run.sh install`) runs ft-gaze and corrects its gaze. It uses SteamVR's combined gaze (mmap set 1), which keeps going when the tracker loses one eye; set 2's combined direction is off by half of whatever the lost eye reads, and the tracker does lose an eye for minutes at a time. It drops blinks (both eyes closing), smooths with a fixation lock, and applies the calibration from the probe (`calibration.json`, reloaded when the probe changes it) plus what the pointer has learned since (`pointer-lessons.json`). It sends the result to the pointer helper 90 times a second. It follows SteamVR's eye tracking log, and when the headset goes back on (SteamVR starts its eye model over, and the error moves), older lessons count less, so the first few after relearn the offset.
-- The pointer helper's **gaze mode** (off by default: `gaze/ft-gazectl on`, `POINTER_GAZE=1` in `~/.config/frametop.conf`, or a button mapped to "Gaze pointer on/off") works like MAGIC pointing (Zhai et al., 1999). The pointer goes where you look. Move the mouse and it's the mouse's, from where the gaze put it, for the last bit. Look well away (5 degrees) and the gaze takes it back. Clicks and drags work as usual.
-- **Learning from nudges:** if the mouse took the pointer from the gaze and moved it a little (0.2 to 8 degrees) before you clicked, you were nudging it onto what you looked at. The helper sends that as a lesson, from the raw gaze when the mouse took over to where you clicked, and ft-gazed learns it. So using it is what calibrates it. `ft-gazectl status` shows the lessons, and `ft-gazectl forget` drops them.
+- The pointer helper's **gaze mode** (off by default: the Gaze page of Frametop Input Settings, `gaze/ft-gazectl on`, `POINTER_GAZE=1` in `~/.config/frametop.conf`, or a mouse or controller button mapped to "Gaze pointer on/off") works like MAGIC pointing (Zhai et al., 1999). The pointer goes where you look. Move the mouse and it's the mouse's, from where the gaze put it, for the last bit. Look well away (5 degrees) and the gaze takes it back. A press isn't sent at once: the pointer stops where the gaze put it, and if that's wrong, drag it onto what you meant with the button still held; the click happens where you let go. To drag something, hold the press still for half a second first (`POINTER_GAZE_HOLD`), then move. Outside games the pointer stays on while gaze mode is on. The dot only shows while the mouse moves it, while a press is held, and as a pulse when you click.
+- **Learning from nudges:** if the mouse took the pointer from the gaze and moved it a little (0.2 to 8 degrees) before you clicked, or you dragged a held press that far, you were nudging it onto what you looked at. The helper sends that as a lesson, from the raw gaze when the mouse took over to where you clicked, and ft-gazed learns it. So using it is what calibrates it. One lesson moves the whole correction by only a third of what it measured (more near where it was taken), since in the first live test one 6 degree lesson moved everything and put the next target 7 degrees off. `ft-gazectl status` shows the lessons, and `ft-gazectl forget` drops them.
 - Nothing writes to SteamVR, its eye tracker, or its files: ft-gaze maps the eye tracker's shared memory read-only. With no fresh gaze (a blink, the service stopped, the headset off), the pointer stays where it is, and the mouse works as always.
 
 Lessons are logged to `pointer-lessons.jsonl`: the raw gaze, the true direction, the correction at the time, and how far off it was.