feat: add latency calibration UI with auto-detection and manual override

[ChuxiJ]

Summary

• Adds latencyMsToSamples() utility to convert latency from milliseconds to audio samples at the current sample rate
• Adds a "Re-detect" button in the Settings dialog Playback Latency section so users can re-measure audio output latency on demand
• Displays latency values in both ms and samples (e.g. "15.0 ms (720 smp)") alongside the active compensation readout with sample rate
• Adds 12 new unit tests covering ms-to-samples conversion, manual override precedence over auto-detected values, compensation seconds, and persistence across normalization calls

Closes #1106

Test plan

• npx tsc --noEmit passes with 0 errors
• npm test passes (17 tests in playbackLatency.test.ts, all green)
• npm run build succeeds
• Open Settings dialog, verify "Playback Latency" section shows detected latency in ms and samples
• Click "Re-detect" button and verify latency values refresh
• Enter a manual override value, save, verify "Manual override" badge appears
• Clear manual override, save, verify it falls back to auto-detected

https://claude.ai/code/session_01KYEjWp985CYRCcSm9J46ps

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