Add smart playlists with full iTunes 12 import (Phase 1)

Auto-populating, criteria-driven playlists that import faithfully from iTunes.

- lintunes/smart.py: recursive SmartCriteria/SmartGroup/SmartRule/SmartLimit
  model (JSON round-tripping), a shared FIELD_REGISTRY used by both the
  evaluator and the editor, and evaluate() (match all/any, nested groups,
  string/int/duration/rating/date/bool ops, "in the last N", limit by
  items/time/size). Null play/skip dates are treated as the distant past,
  matching iTunes.
- iTunes import via a vendored MIT-licensed binary parser
  (lintunes/itunes_smart/, from cvzi/itunes_smartplaylist). Nested groups
  parse and evaluate; blobs we can't represent (MediaKind/iCloud/etc.) flag
  unsupported and keep the imported snapshot. "loved" is dropped per user pref.
- library_manager: create/set/recompute smart playlists (undoable), field-scoped
  coalesced live recompute hooked into the edit/play/skip/add funnels, a no-op
  equality guard to avoid Syncthing churn, and manual-edit guards. main.py
  recomputes on load; conflict_resolver keeps newest criteria for smart lists.
- GUI: ❧ glyph painted in the sidebar branch column, read-only track table for
  smart playlists, New/Edit Smart Playlist menus, and SmartPlaylistEditorDialog
  (per-field rule rows, match all/any, limits, live updating).

Tests: tests/test_round14.py (real captured blobs in tests/smart_blobs.json).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lintunes/storage/conflict_resolver.py

@@ -117,6 +117,13 @@ def _merge_playlist(original_path: Path, conflict_path: Path):
     original = _load_json(original_path)
     conflict = _load_json(conflict_path)
 
+    # Smart playlists: membership is derived, so unioning track_ids would
+    # resurrect tracks that no longer match. Keep the newer file's criteria;
+    # membership is recomputed from it at the next launch.
+    if original.get("playlist_type") == "smart" or conflict.get("playlist_type") == "smart":
+        _keep_newer(original_path, conflict_path)
+        return
+
     # Union track_ids, order from the newer file
     orig_ids = set(original.get("track_ids", []))
     conf_ids = set(conflict.get("track_ids", []))