fix(quick-19): multi-root path resolution for playlist M3U8 tracks

- Replace getLibraryRoot() with getAllLibraryRoots() returning all library paths
- Add resolveM3UPath() for multi-root resolution with knownPaths lookup
- Add toRelativePathMultiRoot() to save relative paths using correct root
- Update removeM3UEntries, replaceM3UEntryPaths, findM3UEntry for []string roots
- Update all 8 call sites in playlist.go for multi-root resolution
- Update existing test signatures for new []string parameter types
- Fix pre-existing golines formatting in scan_queue.go

backend/library/scan_queue.go

@@ -111,7 +111,9 @@ func (l *Library) SoftScanAllLibraries() error {
 	// dynamic library_id unsupported by sqlc. No user input.
 	for _, lib := range libs {
 		result, claimErr := l.db.ExecContext(
-			`UPDATE audio_files SET library_id = ? WHERE library_id = 0 AND file_path LIKE ? || '%'`,
+			`UPDATE audio_files SET library_id = ?`+
+				` WHERE library_id = 0`+
+				` AND file_path LIKE ? || '%'`,
 			lib.ID, lib.Path+"/",
 		)
 		if claimErr != nil {