fix(audio): replace Mutex unwrap with poisoned-mutex recovery (TODO-006)

Replace 42 .lock().unwrap() calls with .unwrap_or_else(|e| e.into_inner())
across 7 files. Poisoned mutex recovery prevents panics in realtime audio
callbacks. Add SAFETY comment to WebRtcFallbackVad Send impl (TODO-007).

crates/chanora_audio/src/sdl_output.rs

@@ -174,7 +174,7 @@ impl AudioCallback for TsPlaybackCallback {
         // in the cpal path, but the upstream design has shipped
         // this way for years.
         {
-            let mut data = self.handler.lock().unwrap();
+            let mut data = self.handler.lock().unwrap_or_else(|e| e.into_inner());
             let _removed_ids = data.fill_buffer(buffer);
             // `_removed_ids` is the list of clients whose stream the
             // handler just finished draining. We could publish that