Fix bounded Opus packet-loss concealment in embedded Linux audio

[zortos293]

Changes

Preserve sender SSRC and RTP timestamp through the embedded Linux audio handoff. Measure unrecovered loss from the RTP timeline and synthesize Opus concealment in valid sample chunks, capped at 100 ms and the existing PCM buffer capacity.

Reset Opus state when the sender source changes, including when a bounded queue drops the first packet from the new source. Decode RED-recovered packets normally without duplicate concealment.

Verification

This republishes unchanged commit d41f07c9ad48fd00bf33ec41346f818eda513234 from #955 after the user-authorized repair of an accidental direct push to dev. The remote target has been restored to 7a76b0c965087750d46411901ce8d04ba1b2524a. This replacement requires review; GitHub's historical merged status on #955 does not mean this change remains on dev.

The orchestrator independently reviewed and tested this exact implementation before the branch repair:

• Real-libopus Linux audio tests: 19 passed, 2 existing device-dependent tests ignored.
• Audio transport regressions: 11 passed.
• Full native streamer workspace tests passed, including 192 transport and 102 Linux platform tests.
• Workspace formatting and Clippy passed.

Regressions cover RTP wrap, short/burst loss, varying packet durations, backward timestamps, source reset, a dropped first packet after source change, and RED recovery. CI will run again on this replacement PR.

Limits

No live GFN session, hardware decode, or real playback-device packet-loss test was available. The evidence is transport and real-libopus regression testing, not live gameplay validation. Audio-only failure isolation is a separate dependent change. No UI or FFI ABI changes.

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