[agency] Harden CLJS eye/head tracking around scheduled snippets

[meekmachine]

Goal

Finish Eye/head tracking as the production facade over CLJS scheduled snippets, with the experimental scheduled-animation behavior as the only path.

Current state

Polyester has src-cljs/latticework/eye_head_tracking.cljs, which delegates much of the planning shape to gaze and emits stable snippets for eyeYaw, eyePitch, headYaw, headPitch, and headRoll. The old TypeScript service still contains more sensor/lifecycle behavior, but worker code must remain planner-only.

This mirrors the Latticework research issue: meekmachine/Latticework#33.

Clojure-way direction

• Main thread owns mouse events, webcam/video, camera-relative calculations, face tracking, requestAnimationFrame, and Loom3 mutation.
• CLJS owns config, target smoothing, throttling, trajectory state, enabled/disabled state, return-to-neutral, and snippet construction.
• Head/eye outputs must go through Animation agency scheduling, not direct AU or bone mutation.
• Disabling head or eye tracking must schedule/remove/reset the relevant snippets so stale pose does not linger.

Acceptance criteria

• Manual targets emit the same AU pairs: 61/62, 64/63, 51/52, 54/53, 55/56.
• Output snippets preserve current priorities, stable names, inherited first frames, and mixerClampWhenFinished behavior.
• headTrackingEnabled: false stops future head snippets and clears any active head pose/transition.
• Return-to-neutral reliably schedules neutral eye/head snippets and is testable.
• Direct engine paths are absent from worker code.
• Existing eye/head public API remains source-compatible through the Polyester adapter.