Gaze mode is a mouse feature: drop its controller parts

Steam reads the Frame controllers itself, outside SteamVR's bindings, and every
press and release it sees takes SteamVR out of laser mode, so controller clicks
at the gaze can't be done cleanly (docs/gaze-controllers.md, from the gaze-first
branch's tests).

- Gaze precision and Gaze drag take a mouse button or a key combination only;
  the controller source, its aim steering, and POINTER_PRECISION_GAIN,
  POINTER_PRECISION_DEADZONE and POINTER_GAZE_DRAG_GAIN are gone.
- The gaze actions (including Gaze pointer on/off) can't be mapped to controller
  buttons: the relay ignores them there and doesn't ask the helper for those
  buttons, and Input Settings no longer offers them.
- Last used wins in gaze mode too: picking up a controller hands it the laser,
  as docs/design.md already said.
- The gaze dot shows all the time (POINTER_GAZE_DOT=always, the default;
  moving brings back the old behaviour), with a switch on the Gaze page.

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

session/frametop.conf.example

@@ -31,11 +31,9 @@ POINTER_GAZE=0             # 1 = the pointer goes where you look, the mouse does
 POINTER_GAZE_RETAKE=5      # gaze mode: how far (degrees) you look away from the pointer before the gaze takes it back from the mouse
 POINTER_GAZE_NUDGE_MAX=8   # gaze mode: a mouse nudge up to this far (degrees) before a click is learned as the eye tracker's error
 POINTER_GAZE_HOLD=0.5      # gaze mode: a press held this long (s) without moving becomes a real press (to drag); moved or released sooner, it clicks where you let go
-POINTER_GAZE_SHOW=1        # gaze mode: the dot shows this long (s) after the mouse moves it; also while a press is held, and a pulse per click
+POINTER_GAZE_DOT=always    # gaze mode: the dot shows all the time (always) | only while the mouse moves it (moving)
+POINTER_GAZE_SHOW=1        # gaze mode, with POINTER_GAZE_DOT=moving: the dot shows this long (s) after the mouse moves it; also while a press is held, and a pulse per click
 POINTER_GAZE_MOUSE=precision # gaze mode: the left button holds back its press, the mouse steers, the release clicks (precision) | clicks right away (direct)
-POINTER_PRECISION_GAIN=0.5  # gaze precision (a button mapped to gaze_precision): the pointer turns this times the controller's turn
-POINTER_PRECISION_DEADZONE=0.3 # gaze precision: degrees the controller turns before the pointer does (the press's own jolt)
-POINTER_GAZE_DRAG_GAIN=1   # gaze drag (gaze_drag): the pointer turns this times the controller's turn
 GAZE_TRACKER=steam         # gaze service: steam = SteamVR's eye tracker | own = our own (gaze/tracker: its frame grabber needs gaze/tracker/install.sh; calibrated in the gaze probe with Own tracker)
 GAZE_EYE=auto              # gaze service: eye bias. auto = each eye weighted by how far off it was at your recent nudges | left | right = that eye counts twice
 HANDS_SWAP_SIDES=0         # hand tracking (hands/run.sh install): 1 = the side cameras' names are swapped, which some SteamVR restarts cause (hands/tools/check_sides.py --ring tells)