Bring the docs up to date with the code

- floating-windows.md and profiles.md describe what's built, with what
  isn't listed as such; the plans, phases, and branch notes are gone
- hands-migration.md is gone: the move is done; its open items are in
  hands/README.md's Known issues
- reference.md: Layout & profiles, every action, key combinations,
  floating windows, the gaze pointer, and hand tracking as they are
- design.md gets the KWin findings from floating-windows.md
- README, gaze/README, AGENTS, hazards, gaze-controllers, and the
  example config catch up with gaze, hands, and the stuck-key fix

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

AGENTS.md

@@ -25,8 +25,8 @@ scripts/frame.sh --host '<cmd>'          # runs on the SteamOS host
 A Steam Frame is someone's personal headset, and they may be wearing it while you work.
 
 - Don't kill or restart `gamescope`, `steam`, `vrserver`, `vrcompositor`, the gamescope session, or the Frametop desktop without asking. Each one ends or disrupts whatever is happening in VR.
-- Don't run host `sudo`, `steamos-readonly disable`, `steamos-devmode` changes, pacman installs, or reboots without explicit approval. Only the Bluetooth fixes need host `sudo`, and they ask.
-- Write only inside the repo, `/tmp`, and the container unless told otherwise. The installers are the exception: they write the user services, launchers, and the SteamVR driver into the home folder.
+- Don't run host `sudo`, `steamos-readonly disable`, `steamos-devmode` changes, pacman installs, or reboots without explicit approval. Three installers need host `sudo`, and they ask for it: the Bluetooth fixes (`setup/bluetooth/install.sh`), hand tracking (`hands/run.sh install` and `caps`, which set ft-camd's file capabilities with `setcap`), and our own eye tracker's frame grabber (`gaze/tracker/install.sh`).
+- Write only inside the repo, `/tmp`, and the container unless told otherwise. The installers are the exception: they write the user services, launchers, and the SteamVR driver into the home folder. The Bluetooth fixes and the eye tracker's frame grabber also install root-owned files and system services under `/etc` (`/etc/steamframe`, `/etc/frametop`, `/etc/systemd/system`).
 - Never copy `.netrc`, SSH keys, or Steam config off the Frame or into this repo.
 
 ## SteamOS updates