fix(audio): properly suppress unused-variable warning for DecodeError msg

Use `let _ = msg` under `#[cfg(not(debug_assertions))]` so the binding
remains available in debug builds for the eprintln! format string.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src-tauri/src/audio.rs

@@ -1149,7 +1149,9 @@ impl Iterator for SizedDecoder {
                         self.current_frame_offset = 0;
                         break;
                     }
-                    Err(symphonia::core::errors::Error::DecodeError(ref _msg)) => {
+                    Err(symphonia::core::errors::Error::DecodeError(ref msg)) => {
+                        #[cfg(not(debug_assertions))]
+                        let _ = msg;
                         self.consecutive_decode_errors += 1;
                         // Log sparingly: first drop, then every 10th to avoid spam.
                         #[cfg(debug_assertions)]