v0.7.0: startup speed — the 21k-track library stops freezing

Three reported symptoms, one shape: every operation was whole-library,
whole-file, on the Qt main thread. Measured on the real library (21,482
tracks, 506 playlists, 15 MB library.json).

The track table sorted through a QSortFilterProxyModel, which asks data()
for a value on every comparison — 580k Python round trips, 8.5 s per table
load, paid again on every reload. TrackTableModel now keeps _tracks in
canonical (playlist) order plus an _order index list and sorts a key list
computed once per track. Nothing used the proxy's filtering. Sorting by #
is the identity order, so "source row" still means "playlist position" for
drag-reorder. 8.5 s -> 0.13 s; MainWindow() 18.1 s -> 0.79 s.

Smart rules compile to closures once per evaluate() instead of being
re-dispatched per track — the operator lookup, casefolding the query and
parsing the rule's own date constants all leave the 21k-iteration loop
(_match_date was re-parsing its own constant 21,482 times per rule).
Verified identical membership against the old evaluator on all 20 real
smart playlists. 2.54 s -> 0.72 s, and it now runs after the first paint.

Also: _reconcile_track skips two to_dict() round trips per unchanged track
(MERGEABLE_FIELDS in the resolver is the single source of truth for what a
merge touches); no git subprocess on the startup path (Updater.enabled is
probed lazily on the background thread, version-button tooltip deferred);
and .resolved/ is pruned to the newest 10 snapshots — it had reached 1.7 GB
across 73 snapshots inside the Syncthing share.

Time to interactive window ~15 s -> 3.2 s. The mid-session freeze when
Syncthing delivers a change — a full reload + recompute + table rebuild
with the window already on screen, which is what GNOME was offering to
force-quit — ~16 s -> 3.8 s.

The merge rework itself (playlist ordering, per-machine play journal,
quieting the dialog) is queued in TASKS.md as Round 36.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

tests/test_round12.py

@@ -24,8 +24,7 @@ def _manager(tmp_path, n=4):
 
 def _select_source_row(table, source_row):
     """Select the visual row backing a given source-model row (sort-proof)."""
-    proxy_index = table.proxy.mapFromSource(table.model_.index(source_row, 0))
-    table.selectRow(proxy_index.row())
+    table.selectRow(table.model_.display_row(source_row))
 
 
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