fix(settings): withhold the Xtream catalog at relock time, keep exact M3U titles in backups, roll back a failed relock-timeout save

- A relock now fails closed immediately: the selected detail is stepped
  off against the lock store, the catalog lists and stored search results
  are emptied, and the filtered reloads publish only while the captured
  lock version is still current.
- Backups carry M3U lock titles verbatim (exact dedup), since the locks
  match group titles exactly.
- A relock-timeout write that fails reverts the in-memory value and shows
  the settings save-failure snackbar.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/architecture/parental-lock.md

@@ -151,7 +151,14 @@ on either side.
   in-portal search (`XtreamStore.refreshSearchResults`, the last
   `searchContent` call as issued) — `searchResults` is a separate array the
   search page renders directly and would otherwise keep locked titles until
-  the query changes. Both reloads fail closed: a category reload that
+  the query changes. A RELOCK fails closed at once rather than after the
+  database answers: the selected detail is stepped off synchronously when
+  the lock store already names its category (the pre-reload category list
+  maps Electron's row id to the provider id), then `withholdCatalog()`
+  empties every catalog list and `clearSearchResults()` the stored search
+  before the filtered reads refill them; both reloads take a publish guard
+  answered before every state patch, so a read issued under an older lock
+  version is dropped instead of published. Both reloads fail closed: a category reload that
   rejects empties the three category lists, and a per-type content reload
   that rejects empties that type and sets it back to `idle` so the next
   visit loads it again (filtered) — rows read under the previous lock state
@@ -246,7 +253,10 @@ on either side.
   its candidates through the capability-selected data source
   (`IXtreamDataSource.getAllCategories`, which the PWA source answers from
   its session cache or the API), so PWA users can set locks too; the
-  hide/show checkboxes remain Electron-only. The M3U dialog hands its lock
+  hide/show checkboxes remain Electron-only. The relock timeout persists
+  through the same undo-on-failure pattern as the switch
+  (`setRelockMinutes` reverts the in-memory value and the facade shows the
+  settings save-failure snackbar). The M3U dialog hands its lock
   list back to `ChannelListContainerComponent`, which awaits the write and
   reports a failed save in a snackbar (the dialog has closed by then). On
   Electron the `categories.locked` re-stamp (`setCategoryLocks`) clears and
@@ -268,6 +278,11 @@ on either side.
 
 ## Backup
 
+M3U group titles travel verbatim (`normalizeParentalLockGroupTitles`, exact
+dedup): locks match `channel.group.title` exactly, so the trimming
+`uniqueStrings` used for favorites would weaken a lock on a title with
+surrounding whitespace.
+
 `lockedGroupTitles` (M3U), `lockedCategories` (Xtream `{categoryType,
 xtreamId}`, Stalker `{categoryType, categoryId}`) travel in each entry's
 `userState`, written only when the playlist has locks. Absent means "no