fix(handtracking): stabilize provider root and linger enabled

(1) HandTrackingProvider always renders the same JSX root
(HandTrackingRuntime) so toggling `enabled` no longer remounts the
<Canvas> below — that remount was destroying the WebGL context every
time the player entered an interaction zone.

(2) Add HAND_TRACKING_LINGER_MS (2s) cooldown on `enabled` so brief
walk-throughs of a trigger zone don't tear down MediaPipe before it
has time to initialize the webcam + model + first frame (cold start
~800ms).

Resolves the WebGL context lost + respawn loop and restores visible
hand tracking in the backend runtime. Browser JS runtime detection
quality is a separate follow-up.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/data/handTrackingConfig.ts

@@ -14,3 +14,9 @@ export const HAND_TRACKING_BROWSER_DELEGATE: "CPU" | "GPU" = "CPU";
 // Absorbs React StrictMode's mount/unmount/mount cycle in dev and rapid
 // `nearby` toggles at trigger borders. Invisible to the user (~5 frames).
 export const HAND_TRACKING_RUNTIME_START_DELAY_MS = 80;
+
+// How long the hand tracking stays active after the trigger condition
+// (nearby / holding / repair step) turns off. Gives MediaPipe enough time
+// to initialize webcam + model + first frame inference before we cleanup,
+// so the user actually sees their hands when entering a zone briefly.
+export const HAND_TRACKING_LINGER_MS = 2000;