feat(comments): add CommentThread, annotation panel, Diskussion section, and i18n keys

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

frontend/src/lib/components/AnnotationCommentPanel.svelte

@@ -0,0 +1,90 @@
+<script lang="ts">
+import CommentThread from './CommentThread.svelte';
+import { m } from '$lib/paraglide/messages.js';
+
+type Props = {
+	documentId: string;
+	annotationId: string;
+	canComment: boolean;
+	currentUserId: string | null;
+	canAdmin: boolean;
+	onClose: () => void;
+	onCountChange?: (count: number) => void;
+};
+
+let {
+	documentId,
+	annotationId,
+	canComment,
+	currentUserId,
+	canAdmin,
+	onClose,
+	onCountChange
+}: Props = $props();
+</script>
+
+<!-- Desktop / tablet panel (≥ sm): absolute overlay on the right side -->
+<div
+	class="absolute top-0 right-0 z-50 hidden h-full w-80 flex-col border-l border-brand-sand bg-white shadow-2xl sm:flex"
+>
+	<div class="flex shrink-0 items-center justify-between border-b border-brand-sand px-4 py-3">
+		<h3 class="font-sans text-xs font-bold tracking-widest text-brand-navy uppercase">
+			{m.comment_panel_title()}
+		</h3>
+		<button
+			onclick={onClose}
+			aria-label={m.comment_panel_close()}
+			class="rounded p-1 text-gray-400 transition-colors hover:bg-brand-sand/50 hover:text-brand-navy"
+		>
+			<svg class="h-4 w-4" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+				<path stroke-linecap="round" stroke-linejoin="round" d="M6 18L18 6M6 6l12 12" />
+			</svg>
+		</button>
+	</div>
+	<div class="flex-1 overflow-y-auto p-4">
+		<CommentThread
+			documentId={documentId}
+			annotationId={annotationId}
+			canComment={canComment}
+			currentUserId={currentUserId}
+			canAdmin={canAdmin}
+			loadOnMount={true}
+			onCountChange={onCountChange}
+		/>
+	</div>
+</div>
+
+<!-- Mobile modal (< sm): fixed full-screen with slide-up sheet -->
+<div class="fixed inset-0 z-50 flex flex-col sm:hidden">
+	<!-- Semi-transparent backdrop -->
+	<div class="flex-1 bg-black/40" onclick={onClose} role="presentation"></div>
+
+	<!-- Slide-up panel -->
+	<div class="flex max-h-[80vh] flex-col rounded-t-2xl bg-white shadow-2xl">
+		<div class="flex shrink-0 items-center justify-between border-b border-brand-sand px-4 py-3">
+			<h3 class="font-sans text-xs font-bold tracking-widest text-brand-navy uppercase">
+				{m.comment_panel_title()}
+			</h3>
+			<button
+				onclick={onClose}
+				aria-label={m.comment_panel_close()}
+				class="rounded p-1 text-gray-400 transition-colors hover:bg-brand-sand/50 hover:text-brand-navy"
+			>
+				<svg class="h-4 w-4" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2">
+					<path stroke-linecap="round" stroke-linejoin="round" d="M6 18L18 6M6 6l12 12" />
+				</svg>
+			</button>
+		</div>
+		<div class="flex-1 overflow-y-auto p-4">
+			<CommentThread
+				documentId={documentId}
+				annotationId={annotationId}
+				canComment={canComment}
+				currentUserId={currentUserId}
+				canAdmin={canAdmin}
+				loadOnMount={true}
+				onCountChange={onCountChange}
+			/>
+		</div>
+	</div>
+</div>