- 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