feat(audio): add weapon aim lock and stance change audio assets for #440
Delivers final 2/6 interaction UI audio assets, completing ticket #440:
- sfx_weapon_aim_lock.ogg (0.5s, clinical targeting lock tone)
- sfx_stance_change.ogg (0.35s, soft mechanical stance toggle click)
Both insert-tech aesthetic, UI Sounds bus, non-positional. Generated
via Stable Audio Open, trimmed, LUFS-normalized, converted to ogg.
Updated docs/assets/audio/ui.md with UI-007 and UI-008 entries.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>