feat(admin): archived-items page with purge dates, restore, and purge

Admins need to see what the archive lifecycle is holding: a dedicated
/admin/archived page listing every hidden item (archived or still in
the missing grace window) with library, file path, status, and - when
retention is enabled - the exact date it will be permanently deleted
(archived_at + ARCHIVE_RETENTION_DAYS).

Per row: Restore (POST /api/media-items/:id/unarchive, clears the
archive state so it reappears; if the file is still gone the next scan
hides it again) and Delete (existing DELETE endpoint for single-row
purge with its reading history). Purge All Archived reuses the existing
bulk button. The library admin banner links to the page and keeps its
purge button; row actions use data attributes with delegated listeners
in admin.ts since this templ version has no JSFunctionCall helper.

Verified live: page 200 with purge dates shown, unarchive returned 204
and reset the row, per-item delete and bulk purge ({purged:1}) both
removed their rows with no leftovers.

templates/admin_library.templ

@@ -38,17 +38,22 @@ templ AdminLibrary(user User, libraries []LibraryData, users []User, archivedCou
 						<div class="card p-4 mb-6 flex items-center justify-between gap-4 flex-wrap">
 							<div>
 								<p class="font-semibold" style="color: var(--text-primary)">
-									Archived items: { archivedCount }
+									<a href="/admin/archived" class="hover:underline" style="color: var(--text-primary); text-decoration: none;">
+										Archived items: { archivedCount }
+									</a>
 								</p>
 								<p class="text-sm" style="color: var(--text-secondary)">
 									Files missing from disk for two consecutive scans. Reading history is kept
 									unless purged; items return automatically if their files come back.
 								</p>
 							</div>
-							<button type="button" onclick="purgeArchivedItems()" class="btn btn-secondary">
-								@Icon("trash", "h-4 w-4")
-								Purge Archived Now
-							</button>
+							<div class="flex items-center gap-2">
+								<a href="/admin/archived" class="btn btn-secondary">View Archived</a>
+								<button type="button" onclick="purgeArchivedItems()" class="btn btn-secondary">
+									@Icon("trash", "h-4 w-4")
+									Purge Archived Now
+								</button>
+							</div>
 						</div>
 					}
 					<div id="libraries-container">