fix(cache): make shared cache state survive a second instance

Installing a second LoRA Manager instance (standalone or a second
ComfyUI install) that shares the settings directory puts two processes
on the same cache databases. Three things made that unsafe.

- The updater preserved cache/ and model_cache/ but not a legacy
  recipe_cache/ directory, so a portable install predating the cache/
  move lost its recipe database on a git-based update. Add it to
  _PRESERVE_DIRS and to .gitignore.
- Cache connections used the sqlite3 default 5s timeout, which a
  scanning instance can exceed, turning a concurrent write into
  "database is locked". Route every shared cache connection through
  connect_cache_db(), which raises the timeout to 30s and sets
  busy_timeout + synchronous=NORMAL to match the existing WAL mode.
  App-private databases (download queue, update history) are unchanged.
- A full-table cache replace is a read-modify-write that SQLite cannot
  make atomic across processes, so two instances could interleave and
  one snapshot could overwrite the other. Guard the recipe and model
  save_cache paths with a cross-process advisory lock (flock on POSIX,
  msvcrt on Windows). Locking is best-effort: if it is unavailable the
  call proceeds and the SQLite busy timeout is the fallback.

The lock file is a hidden sibling of the database and is deliberately
never unlinked, so a second process cannot lock a fresh inode.

py/routes/update_routes.py

@@ -21,7 +21,20 @@ NETWORK_EXCEPTIONS = (ClientError, OSError, asyncio.TimeoutError)
 # otherwise delete them because they are untracked and, in released tags,
 # not listed in ``.gitignore``. ``-e`` excludes a path from cleaning
 # regardless of whether it is ignored.
-_PRESERVE_DIRS = ('settings.json', 'civitai', 'wildcards', 'backups', 'stats', 'logs', 'cache', 'model_cache')
+# ``cache`` covers the resolved cache tree (cache/model, cache/recipe,
+# cache/fts, ...); the legacy ``recipe_cache`` / ``model_cache`` directories
+# are listed too because a portable install can predate the cache/ move.
+_PRESERVE_DIRS = (
+    'settings.json',
+    'civitai',
+    'wildcards',
+    'backups',
+    'stats',
+    'logs',
+    'cache',
+    'model_cache',
+    'recipe_cache',
+)
 
 
 def _clean_excludes() -> List[str]: