fix(rendering): open recordings with an unreadable mic track

[richiemcilroy]

Summary

Investigating #2069 (claimed 0-byte audio-input.ogg files in studio mode) showed the reported mechanism cannot occur, but it surfaced a real robustness gap: the editor refused to open an entire recording when the mic track is unreadable, even though the display and camera tracks decode fine. The single-segment path even panicked.

Changes

• crates/rendering/src/project_recordings.rs: an unreadable mic file now degrades to "no mic audio" with a warning instead of failing (or panicking on) the recording open. This mirrors the existing system-audio handling from fbc8755 and matches playback, which already degrades a broken mic track in loaded_track. Export is untouched and keeps failing loudly rather than silently dropping a track.
• crates/enc-ffmpeg/src/mux/ogg.rs: regression tests pinning the OggFile/OpusEncoder path the issue claimed was broken: 5s of 96kHz mono input produces a playable file of the right duration, sub-frame input is flushed at finish rather than dropped, and a zero-frame track still writes container header pages instead of a 0-byte file.

Verification

• cargo test -p cap-enc-ffmpeg: all 49 tests pass, including the 3 new ones.
• cargo check -p cap-rendering -p cap-editor -p cap-export clean; clippy clean for the touched code.
• End-to-end: cloned a real studio + camera bundle and truncated segment-0/audio-input.ogg to 0 bytes. Before this change the open fails with "segment 0 / mic / Failed to open audio: End of file"; after it, the recording opens and renders frame 0, with a warning logged.

Greptile Summary

This PR makes editor rendering tolerate unreadable microphone tracks while preserving strict audio validation during export.

• Converts failed microphone metadata loads into an absent optional track with a warning in both single- and multi-segment recordings.
• Adds Ogg/Opus regression coverage for sustained 96 kHz input, sub-frame flushing, and empty-track container headers.

Confidence Score: 5/5

The PR appears safe to merge with no actionable defects identified.

The editor now degrades only the optional microphone metadata track when loading fails, while required display media and export-time audio validation retain their existing failure behavior; the added encoder tests align with the current Ogg and Opus lifecycle.

Important Files Changed

Filename	Overview
crates/rendering/src/project_recordings.rs	The mic fallback is consistent across recording formats, retains required display-based timing, and does not weaken export’s separate strict audio validation.
crates/enc-ffmpeg/src/mux/ogg.rs	The new tests exercise sustained resampling, short-input flushing, and zero-frame Ogg initialization using the existing encoder and muxer contracts.

_{Reviews (1): Last reviewed commit: "fix(rendering): open recordings with an ..." | Re-trigger Greptile}

Context used:

• Knowledge Base — Export and Rendering Pipeline

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