Launch apps floating, remember where they floated, and Launch as Standalone

ft-float launch APP / run COMMAND: ft-floatd starts the app and floats its
first window (matched by process or desktop file name for 30 s) where that
app last floated, or in front of you at the primary screen's density. Each
app's place (pose relative to the primary screen, size in pixels, scale) is
kept in ~/.config/frametop-float.json whenever one of its windows stops
floating; the scale isn't applied yet, since rescaling can loop (written up
in docs/floating-windows.md, Known problems).

Launch as Standalone (float/ft_apps.py): the session writes copies of the
apps' desktop files with that action and puts them first in XDG_DATA_DIRS,
so it shows in the Application Launcher's and the taskbar's right-click menus
in the Frametop desktop only. ft-floatd rewrites them when apps change.

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

docs/floating-windows.md

@@ -11,8 +11,13 @@ Built so far (2026-09-29; the KWin side tested on the headless test desktop, `sc
 - The 3D mouse's drag lock crosses onto other Frametop panels (not while carrying one).
 - The float key (2026-09-30): the input relay's `float_toggle` (Meta+Shift+F by default) and `dock_all`, through `float pointer` and `dock all` on ft-floatd. Tested on the headless desktop.
 - The title bar button (2026-09-30, branch `float-titlebar`): `decoration/` (Frametop's QML window decoration, installed by the session script; `decoration/apply.sh` switches the running desktop to it or back to Breeze), and keep-below as the floating flag in the script. Tried on the live desktop: the button floats Dolphin and docks it again, the float key and `dock all` keep the flag in step, and maximized windows look right.
+- Launching floating (2026-09-30, branch `float-launch`): `ft-float launch APP` and `ft-float run COMMAND`, matching the new window by process (or a child) or by desktop file name for 30 seconds, and each app's remembered place (pose relative to the primary screen, size in pixels, scale) in `~/.config/frametop-float.json`, kept whenever one of its windows stops floating. With nothing remembered, the window opens in front of you, at the primary screen's density, 0.8 to 2 m away. Launch as Standalone (`float/ft_apps.py`): the session writes the desktop file copies and puts them first in `XDG_DATA_DIRS`; ft-floatd rewrites them when apps change. Tried on the live desktop: Dolphin launched floating, came back at its remembered pose after closing, and Konsole floated from `ft-float run`; the right-click entry needs a desktop start to show. The remembered scale is kept but not applied yet (see Known problems).
 
-Not built yet: phase 2 (the ghost, tear-off by dragging, push-flush docking), phase 3 (launching floating, Launch as Standalone, remembered placement), and phase 4.
+Not built yet: phase 2 (the ghost, tear-off by dragging, push-flush docking), the rest of phase 3 (new windows of a floating app placed where that app's last went), and phase 4.
+
+Known problems:
+
+- **Changing a floating window's scale can loop** (Meta+scroll, or the scale buttons). Seen on the live desktop on 2026-09-30 with Dolphin at 1.2: the window flipped between 1187 and 1424 logical pixels wide, and its output between 1687 and 1925, several times a second, until it was closed. The cause looks like this: when an output resizes, KWin resizes a window on it to keep its distance from both edges. `follow` then resizes the output from a window size that's already stale. The next output change resizes the window again, and the two stay one step out of phase. To fix: have ft-floatd own the window's size while it floats. After resizing the output, treat a window change by the same amount as KWin's echo and put the window back, instead of following it. Until then, a launched app doesn't get its remembered scale back.
 
 Build order from 2026-09-30, each merged into `experimental` when done: (1) the float key and docking everything, (2) the title bar button, (3) phase 3, (4) hiding screens one at a time, (5) profiles (`docs/profiles.md`).