Modernize gaze runtime path

[meekmachine]

Summary

• Route eye/head gaze state, config, and lifecycle through the modern GazeService path.
• Use the animation-agency scheduler as the preferred GazeRuntime when an animation agency is present, so gaze output mixes with other Loom3 snippets instead of writing AUs directly.
• Keep direct transitionContinuum output only as the fallback path when no animation agency is available.
• Preserve the production experimental target filtering defaults (smoothFactor: 0.25, minDelta: 0.01) so high-frequency pointer/webcam noise is damped before it reaches Loom3.
• Upsert repeated eye/head tracking snippets by name without explicitly removing them first, allowing inherited first keyframes to resolve from the live pose without a mixer gap.
• Clear disabled gaze channels immediately: disabling head tracking removes head snippets and schedules neutral head yaw/pitch/roll snippets without disturbing eye tracking.
• Force a camera-relative apply when eye/head channels are enabled so newly enabled head tracking catches up even if the shared gaze target did not move.
• Keep gazeMode and useAnimationAgency as deprecated compatibility fields, and document the new architecture.
• Add focused tests for GazeService planning/runtime behavior, scheduler-backed gaze output, channel disable cleanup, and camera-relative channel enable catch-up.

Closes #15
Refs #12

Verification

• npm run typecheck
• npm run build
• npm test
• npm test -- --run src/eyeHeadTracking/__tests__/eyeHeadTrackingService.test.ts src/eyeHeadTracking/__tests__/eyeHeadTrackingScheduler.test.ts src/gaze/__tests__/service.test.ts

[meekmachine]

Companion LoomLarge UI/profile PR is open here: meekmachine/LoomLarge#578.

It persists profile.eyeHeadTracking settings in character profiles and routes the app/module UI through the modern gaze runtime path from this Latticework PR.