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/host/+page.svelte

@@ -9,6 +9,7 @@
 	import ConfirmSheet from '$lib/components/ConfirmSheet.svelte';
 	import Modal from '$lib/components/Modal.svelte';
 	import IconButton from '$lib/components/IconButton.svelte';
+	import { commentsEnabled } from '$lib/event-config-store';
 
 	interface UserSummary {
 		id: string;
@@ -448,9 +449,10 @@
 			Benutzer sperren
 		</h2>
 		<p class="mb-4 text-sm text-gray-600 dark:text-gray-400">
-			<strong>{banTarget.display_name}</strong> wird gesperrt: alle Uploads verschwinden aus Galerie,
-			Diashow und Export, und Hochladen, Liken und Kommentieren werden blockiert. Der Lesezugriff (Feed
-			ansehen, Keepsake herunterladen) bleibt bestehen. Rückgängig machbar über „Entsperren“.
+			<strong>{banTarget.display_name}</strong> wird gesperrt: alle Uploads verschwinden aus
+			Galerie, Diashow und Export, und Hochladen, Liken{$commentsEnabled ? ' und Kommentieren' : ''} werden
+			blockiert. Der Lesezugriff (Feed ansehen, Keepsake herunterladen) bleibt bestehen. Rückgängig machbar
+			über „Entsperren“.
 		</p>
 		<div class="flex gap-2">
 			<button onclick={() => (banTarget = null)} class="btn btn-secondary flex-1">
@@ -823,7 +825,7 @@
 															onclick={() =>
 																(confirmAction = {
 																	title: 'Sperre aufheben?',
-																	message: `${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)