Both machines now reflect each other's changes within a couple seconds, and
genuine Syncthing conflicts auto-merge with a backup and an alert.
- sync_watcher.py: QFileSystemWatcher (debounced, re-arms after atomic renames)
emits a single `changed`; the manager decides if it was external.
- library_manager: `reload_from_disk()` re-reads and reconciles disk into memory
(max play/skip counts, newest edit wins, playlist membership unioned), keeping
local unsaved edits and object identity so open views stay valid, then refreshes
the UI without touching the player. `flush()` records each file's (mtime, size)
so our own writes are never mistaken for an external change. New signals
library_reloaded / conflict_resolved.
- conflict_resolver: back up BOTH sides into .resolved/<ts>/{original,incoming}/
before merging, return list[ConflictSummary], add restore_backup(); runs at
startup and live.
- gui/conflict_dialog.py: modeless summary with Open/Restore backup; main_window
shows it from a status-bar notice and preserves scroll+selection on reload.
Tests: tests/test_round16.py (9) + full suite green (225).
Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
