Refresh QuestCameraKit and consolidate native QR tracking

[xrdevrob]

QuestCameraKit now targets Unity 6000.3.12f1 and updated Meta/OpenXR/Inference packages, installs its dependencies from a fresh clone, and includes a combined app with a simple controller-driven sample menu. QR tracking uses Meta MRUK exclusively; the old ZXing sample and dependency have been removed while preserving the native scene and prefab GUIDs.

The maintenance commits also fix camera startup guards, inference resource cleanup and capture-pose placement, stereo WAV truncation, microphone/request lifecycle issues, JSON escaping, and WebRTC setup. Tracked credential values were replaced with placeholders; ImageLLM and WebRTC require private test configuration.

Validation and merge gates:

• Repository integrity, dependency-lock agreement, source archive, Unity regression checks, and seven-scene missing-script audit pass.
• Seven checked-in Quak plans validate with 0.4.0-alpha.1. Native QR acceptance requires an actual MRUK QR trackable; startup checks do not prove controller navigation or recognition accuracy.
• All seven final Android ARM64 IL2CPP development builds pass: combined app plus six individual headset samples. GitHub repository checks and CodeQL analysis pass.
• Keep this draft until the Quest 3S is awake/unlocked and actual camera, native QR, scene navigation, and visual checks pass. The final combined APK installed on Quest 3S, but Quak exited with code 2 at SensorLockActivity before sample execution. ImageLLM cloud/microphone and WebRTC peer workflows also remain unverified; compilation is not their acceptance evidence.

Commits are separated into dependency/sample maintenance, the menu, native QR consolidation, native overlay/lifecycle corrections, and stronger acceptance checks. See docs/testing.md for reproducible commands and explicit limits.