Fix and expand tests: 63 tests passing, covers all core modules

Remove tests/ from .gitignore (was accidentally excluded).

- test_ripper.py: rewrite for current API (_parse_cddb_lines,
  _extract_tracks, _rename_files, _clean_input); fix default quality
- test_organizer.py: update filename assertions (spaces→underscores);
  add TestSanitizeFilename, TestCheckDiscCounts, in-place mode
- test_playlist.py: fix dummy filenames to underscore scheme;
  add multi-disc, filename sanitization, EXTINF and fallback tests

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

.gitignore

@@ -12,7 +12,6 @@ dist/
 
 idea/
 .idea/
-tests/
 testdata/
 CLAUDE.md