feat: Latency calibration UI with auto-detection and manual override

[ChuxiJ]

Problem

Audio output latency is not measured or compensated. This causes:

1. Recording offset: Recorded audio is misaligned with the grid by the output latency amount
2. Visual desync: Playhead position doesn't account for audio pipeline delay
3. Live monitoring: Input monitoring has uncompensated round-trip latency

Without latency calibration, recording is unreliable and users cannot trust timing.

Proposed Solution

1. Auto-detect: Read AudioContext.baseLatency + AudioContext.outputLatency on context creation
2. Display: Show detected latency in Settings panel (in ms and samples)
3. Manual override: Allow users to enter custom latency value (for external audio interfaces)
4. Compensation: Offset recorded audio by the calibrated latency amount
5. Visual compensation: Adjust playhead rendering to account for output latency

Technical Notes

• Reference: TASK_QUEUE.md Sprint 2 backlog item
• Key files: src/engine/AudioEngine.ts, src/components/dialogs/SettingsDialog.tsx
• baseLatency supported in Chrome/Firefox/Safari; outputLatency Chrome-only
• For unsupported browsers, fall back to manual entry with sensible default (10ms)

Acceptance Criteria

• Settings panel shows detected audio latency
• Users can manually override latency value
• Recorded audio clips are offset-corrected by latency amount
• Latency value persists across sessions
• Fallback for browsers without outputLatency API
• Unit test for latency compensation calculation