feat(audio): save recordings as Ogg Opus

[pranc1ngpegasus]

Summary

• replace per-source WAV recording with Ogg/Opus (mic.ogg and system.ogg)
• encode off the real-time audio callback through a bounded background queue
• write each completed Opus packet immediately as a checksummed Ogg page
• periodically sync completed pages and finalize the last page with EOS/granule trimming on a clean stop
• retain legacy database field names while storing the new .ogg paths

Why

WAV writes previously happened synchronously on the audio callback and recordings depended on a clean session stop. Ogg page boundaries let completed audio remain independently recoverable when a session or process terminates unexpectedly, while Opus substantially reduces recording size.

Impact

New sessions store separate microphone and system recordings as Ogg/Opus. A clean stop drains the bounded queue and writes EOS; an abnormal stop leaves the already completed pages readable without requiring a post-processing concatenation step.

Validation

• swift build
• cargo fmt --all -- --check
• cargo test -p wisp-core -p wisp-storage -p wisp-audiokit (23 tests)
• generated a 48 kHz Opus/Ogg fixture and verified normal and EOS-truncated variants with macOS afinfo
• full workspace tests are currently blocked in this environment because the Xcode Metal compiler is unavailable