feat: tracklist column reset, device sync cross-platform template fix, filename template builder, privacy policy

- Add "Reset to defaults" button to column picker in AlbumTrackList, PlaylistDetail, Favorites (all 8 locales)
- Fix device sync cross-OS status detection: store filenameTemplate in manifest, use it for path computation on import
- Redesign filename template UI: preset buttons (Standard/Multi-Disc/Alt. Folder), clickable token chips ({artist}, {album}, etc.), clear button
- Fix suggestions section in PlaylistDetail missing album column rendering
- Add PRIVACY.md documenting all third-party integrations (Last.fm, LRCLIB, Apple Music, Discord); link from README

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

src-tauri/src/lib.rs

@@ -1420,9 +1420,9 @@ fn get_removable_drives() -> Vec<RemovableDrive> {
 /// The file records which sources (albums/playlists/artists) are synced to this
 /// device so that another machine can pick them up without relying on localStorage.
 #[tauri::command]
-fn write_device_manifest(dest_dir: String, sources: serde_json::Value) -> Result<(), String> {
+fn write_device_manifest(dest_dir: String, sources: serde_json::Value, filename_template: String) -> Result<(), String> {
     let path = std::path::Path::new(&dest_dir).join("psysonic-sync.json");
-    let payload = serde_json::json!({ "version": 1, "sources": sources });
+    let payload = serde_json::json!({ "version": 1, "sources": sources, "filenameTemplate": filename_template });
     let json = serde_json::to_string_pretty(&payload).map_err(|e| e.to_string())?;
     std::fs::write(&path, json).map_err(|e| e.to_string())
 }