Set execute permissions on ALL files in sidecar dir on Unix

Previously only the main sidecar binary got chmod 755. Now all files
in the extraction directory get execute permissions — covers ffmpeg,
ffprobe, and any other bundled binaries. Applied in three places:
- sidecar/mod.rs: after local extraction
- commands/sidecar.rs: after download extraction
- commands/media.rs: removed single-file fix (now handled globally)

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

src-tauri/src/commands/media.rs

@@ -99,16 +99,6 @@ 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());
             }
         }