fix(settings): offer the portal unlock row in fail-closed mode

When the lock store cannot be read every portal category is withheld
but no locked ids are known, so the rail showed no "Enter PIN to show"
row. It now shows the row without a count in that state.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

docs/architecture/parental-lock.md

@@ -19,7 +19,9 @@ follow in a second PR.
 - The unit of locking is the category. Nothing is blurred or greyed: a
   withheld category and its rows are absent. The only trace is one
   "N locked · Enter PIN to show" row at the bottom of a portal's category
-  rail, which opens the PIN prompt.
+  rail, which opens the PIN prompt. In fail-closed mode (lock store
+  unreadable) the row shows without a count, since which categories are
+  locked is unknown while every one of them is withheld.
 - The unlock lives in memory only. The app locks again on every restart, on
   "Lock now" (header button, command palette, settings), and after
   `Settings.parentalLockRelockMinutes` minutes without user interaction