Add scoped and configurable Unity audio

[liuzqk]

What changed

• add addressable-friendly AudioBankSO assets with stable semantic event ids and scoped registration
• add pooled SFX cooldowns, concurrency limits, priorities, loop stop, and configurable pool sizing
• add two-source intro/loop music with manager defaults and per-track crossfade/fade-out timing
• expose 3D cue pan, rolloff, min/max distance, Doppler, spread, and reverb settings
• make AudioMixer volume conversion reusable and SaveManager persistence optional
• add validation, EditMode/PlayMode coverage, and package setup documentation

Why

GalleryKeeper needs a dependency-light Unity audio backend whose banks can follow Addressables content lifetimes and whose routine content tuning is data-driven, without introducing FMOD or Wwise. The previous package lacked scoped bank registration and several playback controls needed for room content production.

Impact

Existing PlaySFX and PlayMusic entry points remain available. Consumers can load and register an AudioBankSO for a content scope, configure project playback policy through ConfigurePlayback, tune individual cue spatial behavior and music transitions, then stop/unregister the bank before releasing its Addressables handle.

Validation

• Unity 6000.3.10f1, ZE Audio EditMode — 8/8 passed
• Unity 6000.3.10f1, ZE Audio PlayMode batchmode — 5/5 passed
• GalleryKeeper consumer EditMode — 43/43 passed
• GalleryKeeper consumer PlayMode batchmode — 12/12 passed
• repeated GalleryKeeper starter-asset generation changed 0 tuned asset hashes
• git diff --check passed