Click stability: only a hand controller's press starts it

The 3D mouse drives SteamVR's laser through the ft_pointer virtual
controller, so its events reach the screens the same way a controller's
do. The filter held every press, which turned the mouse's short drags
(selecting a character or two, nudging a slider) into clicks. Mark
button events from hand controllers and start the filter only on those.

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

docs/controller-click-stability.md

@@ -6,10 +6,12 @@ zone delivers the click at the original position, even if the hand moved during
 release. Moving outside the zone begins a normal drag immediately; returning to
 the zone does not turn it back into a click. There is no hold-duration timer.
 
-This filters overlay pointer content events on desktop monitors only. Native mouse
-input, SteamVR UI, separate screen grab bars and floating-app title-bar carrying
-are unaffected. Multi-button gestures keep their existing behavior. A motion
-onto another desktop monitor starts a drag; cross-monitor motion is not stabilized.
+This filters overlay pointer content events on desktop monitors only, and only
+presses from hand controllers start it. The 3D mouse (whose laser comes from the
+`ft_pointer` virtual controller), SteamVR UI, separate screen grab bars and
+floating-app title-bar carrying are unaffected. Multi-button gestures keep their
+existing behavior. A motion onto another desktop monitor starts a drag;
+cross-monitor motion is not stabilized.
 
 CLI (runtime preferences, reset to 8 on desktop restart):