Fix ffmpeg permission denied on Linux

The bundled ffmpeg in the sidecar extract dir lacked execute permissions.
Now sets chmod 755 on Unix when find_ffmpeg locates the bundled binary.

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

src-tauri/src/commands/media.rs

@@ -99,6 +99,16 @@ fn find_ffmpeg() -> Option<String> {
             };
             let ffmpeg_path = sidecar_dir.join(ffmpeg_name);
             if ffmpeg_path.exists() {
+                // Ensure execute permission on Unix
+                #[cfg(unix)]
+                {
+                    use std::os::unix::fs::PermissionsExt;
+                    if let Ok(meta) = std::fs::metadata(&ffmpeg_path) {
+                        let mut perms = meta.permissions();
+                        perms.set_mode(0o755);
+                        let _ = std::fs::set_permissions(&ffmpeg_path, perms);
+                    }
+                }
                 return Some(ffmpeg_path.to_string_lossy().to_string());
             }
         }