feat(comments): hide every comment mention when COMMENTS_ENABLED=false

The kill-switch previously left comment UI/text visible in several places.
Sweep the whole surface so a comments-off instance shows no trace:

Frontend (main app):
- VirtualFeed grid tile: gate the comment button/count on $commentsEnabled
  (was ungated — the only feed surface still showing it).
- admin stats: hide the "Kommentare" count card.
- UploadSheet "Uploads geschlossen" notice, host ban-modal description, and
  host/admin unban confirmations: drop the "…und kommentieren" wording.
- export page: drop "Kommentaren" from the keepsake description.

Keepsake export (had no concept of the flag):
- export.rs: thread comments_enabled into the exported data (ViewerEvent),
  wired through spawn_export_jobs/recover_exports and their call sites
  (host.rs, main.rs).
- export-viewer: gate comment counts (list + grid) and the lightbox comments
  section; older exports without the field default to enabled (?? true).

Backend still 403s comment writes when disabled (unchanged) — this is the UI
half so stale clients and archives match.

Verified on the running stack (COMMENTS_ENABLED=false): /event reports
comments_enabled=false, a regenerated keepsake embeds "comments_enabled": false
with no comment UI, and the uploads-closed notice renders "…ansehen und liken."

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

frontend/src/routes/admin/+page.svelte

@@ -8,7 +8,12 @@
 	import Modal from '$lib/components/Modal.svelte';
 	import IconButton from '$lib/components/IconButton.svelte';
 	import { PRESETS, DEFAULT_SEED, buildPaletteCss, type ThemeConfig } from '$lib/theme/palette';
-	import { previewTheme, PALETTE_CACHE_KEY, loadEventConfig } from '$lib/event-config-store';
+	import {
+		previewTheme,
+		PALETTE_CACHE_KEY,
+		loadEventConfig,
+		commentsEnabled
+	} from '$lib/event-config-store';
 	import { onDestroy } from 'svelte';
 
 	interface StatsDto {
@@ -644,12 +649,14 @@
 								</p>
 								<p class="mt-0.5 text-xs text-gray-500 dark:text-gray-400">Uploads</p>
 							</div>
-							<div class="card p-4 text-center">
-								<p class="text-3xl font-bold text-gray-900 dark:text-gray-100">
-									{stats.comment_count}
-								</p>
-								<p class="mt-0.5 text-xs text-gray-500 dark:text-gray-400">Kommentare</p>
-							</div>
+							{#if $commentsEnabled}
+								<div class="card p-4 text-center">
+									<p class="text-3xl font-bold text-gray-900 dark:text-gray-100">
+										{stats.comment_count}
+									</p>
+									<p class="mt-0.5 text-xs text-gray-500 dark:text-gray-400">Kommentare</p>
+								</div>
+							{/if}
 							<div class="card p-4 text-center">
 								<p class="text-3xl font-bold text-gray-900 dark:text-gray-100">
 									{diskPct(stats)} %
@@ -1053,7 +1060,7 @@
 													onclick={() =>
 														(confirmAction = {
 															title: 'Sperre aufheben?',
-															message: `${user.display_name} kann danach wieder hochladen, liken und kommentieren.`,
+															message: `${user.display_name} kann danach wieder hochladen${$commentsEnabled ? ', liken und kommentieren' : ' und liken'}.`,
 															confirmLabel: 'Entsperren',
 															tone: 'default',
 															run: () => unban(user)