Add head follow: the pointer comes along when you turn your head

Off by default. With POINTER_FOLLOW=1 (a switch on the Pointer page of
Frametop Input Settings, or a mouse button mapped to Head follow on/off),
the cursor rides on a reference direction leashed POINTER_LEASH_DEG (10)
from where you face. Within the leash it stays put in the room; past it,
it turns with your head and keeps its offset. A leash of 0 locks it to
your view. Head roll is ignored, the cursor stays within 40 degrees of
the reference, and it holds still in the room while the left button is
down so the head can't nudge a click or a drag.

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

session/frametop.conf.example

@@ -18,6 +18,8 @@ POINTER_LASER_WIDTH=0.8    # controller beam width (dashboard.laserRayWidthScale
 POINTER_ORIGIN_MARGIN=0.15   # the laser starts at least this far (m) in front of its target, so small floating controls stay hittable
 POINTER_SCENE_RADIUS=0.5   # texture-less dashboard overlays (dock, window controls): hit radius (m) around their origin
 POINTER_EDGE_REACH=0.3     # just off a panel, the cursor stays on its plane this far (m), to reach its resize edges and window controls
+POINTER_FOLLOW=0           # 1 = the cursor follows your head on a leash (a mouse button mapped to Head follow on/off toggles it)
+POINTER_LEASH_DEG=10       # head follow: how far (degrees) your head can turn before the cursor comes along; 0 locks it to your view
 META_DASHBOARD=0   # 1 = a Meta tap on a pass-through keyboard toggles the SteamVR dashboard (pointer mode only)
 SHARE_KEYS=0       # 1 = keys of keyboards grabbed for the desktop also go to @frametop_keys, for hotkey tools (any local process can listen)
 LAYOUT_GRAB_OFFSET=0.075   # arranging screens: where the floating window's grab bar is, in metres below the screen