refactor(briefwechsel): ConversationTimeline renders ThumbnailRow per letter

Drops the inline row markup, arrow icons, status-dot helper, and the
otherPartyName helper that only fed it. Each visible row is now a
ThumbnailRow, which owns its own aria-label, border color, meta and
tag rendering. The year-divider and "new document" footer are
untouched — they were always intended to stay as timeline chrome.

Also widens the documents prop shape to include the summary, tags
and thumbnail metadata that ThumbnailRow consumes; the backend
already returns these fields via the Document schema so no server
change was required.

Refs #305

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

frontend/src/routes/briefwechsel/ConversationTimeline.svelte

@@ -1,7 +1,10 @@
 <script lang="ts">
-import { formatDate } from '$lib/utils/date';
 import { m } from '$lib/paraglide/messages.js';
 import DistributionBar from '$lib/components/DistributionBar.svelte';
+import ThumbnailRow from '$lib/components/ThumbnailRow.svelte';
+
+type Person = { id: string; firstName?: string | null; lastName: string; displayName: string };
+type Tag = { id: string; name: string };
 
 interface Props {
 	documents: {
@@ -10,14 +13,15 @@ interface Props {
 		originalFilename: string;
 		documentDate?: string;
 		location?: string;
-		status: string;
+		summary?: string;
-		sender?: {
+		contentType?: string;
-			id: string;
+		thumbnailKey?: string;
-			firstName?: string | null;
+		thumbnailGeneratedAt?: string;
-			lastName: string;
+		thumbnailAspect?: 'PORTRAIT' | 'LANDSCAPE';
-			displayName: string;
+		pageCount?: number;
-		} | null;
+		sender?: Person | null;
-		receivers?: { id: string; firstName?: string | null; lastName: string; displayName: string }[];
+		receivers?: Person[];
+		tags?: Tag[];
 	}[];
 	senderId: string;
 	receiverId?: string;
@@ -54,25 +58,7 @@ const outCount = $derived(documents.filter((d) => d.sender?.id === senderId).len
 const inCount = $derived(documents.length - outCount);
 
 const isBilateral = $derived(!!senderId && !!receiverId);
-
+const showOtherParty = $derived(!receiverId);
-function statusDotClass(status: string): string {
-	const map: Record<string, string> = {
-		PLACEHOLDER: 'bg-brand-sand',
-		UPLOADED: 'bg-brand-mint',
-		TRANSCRIBED: 'bg-brand-mint',
-		REVIEWED: 'bg-brand-navy/70',
-		ARCHIVED: 'bg-brand-navy'
-	};
-	return map[status] ?? 'bg-brand-sand';
-}
-
-function otherPartyName(doc: (typeof documents)[number]): string {
-	if (doc.sender?.id === senderId) {
-		const r = doc.receivers?.[0];
-		return r ? r.displayName : m.conv_no_party();
-	}
-	return doc.sender ? doc.sender.displayName : m.conv_no_party();
-}
 
 const newDocUrl = $derived(
 	`/documents/new?senderId=${encodeURIComponent(senderId)}${receiverId ? `&receiverId=${encodeURIComponent(receiverId)}` : ''}`
@@ -100,50 +86,7 @@ const newDocUrl = $derived(
 			</div>
 		{/if}
 
-		<a
+		<ThumbnailRow doc={doc} isOut={isOut} showOtherParty={showOtherParty} />
-			href="/documents/{doc.id}"
-			aria-label="{doc.title || doc.originalFilename}, {doc.documentDate
-				? formatDate(doc.documentDate)
-				: ''}"
-			class="group flex min-h-[44px] cursor-pointer items-center gap-[9px] border-b border-l-[3px] border-line-2 px-[14px] py-[10px] transition-colors last:border-b-0 hover:bg-muted"
-			class:border-l-primary={isOut}
-			class:border-l-accent={!isOut}
-		>
-			<img
-				src={isOut
-					? '/degruyter-icons/Simple/Medium-24px/SVG/Action/Long-Arrow/Long-Arrow-Right-MD.svg'
-					: '/degruyter-icons/Simple/Medium-24px/SVG/Action/Long-Arrow/Long-Arrow-Left-MD.svg'}
-				alt=""
-				aria-hidden="true"
-				class="h-4 w-4 shrink-0 opacity-60"
-			/>
-
-			<div class="min-w-0 flex-1">
-				<div class="mb-[2px] truncate text-sm font-bold text-ink">
-					{doc.title || doc.originalFilename}
-				</div>
-				<div class="flex items-center gap-[5px] text-sm text-ink-3">
-					<span>{doc.documentDate ? formatDate(doc.documentDate) : '—'}</span>
-					{#if doc.location}
-						<span class="text-line">·</span>
-						<span>{doc.location}</span>
-					{/if}
-					{#if !receiverId}
-						<span class="text-line">·</span>
-						<span>{otherPartyName(doc)}</span>
-					{/if}
-					<span
-						class="ml-[3px] h-[6px] w-[6px] shrink-0 rounded-full {statusDotClass(doc.status)}"
-						title={doc.status}
-					></span>
-				</div>
-			</div>
-
-			<span
-				class="shrink-0 text-sm text-ink-3 opacity-0 transition-opacity group-hover:opacity-100"
-				aria-hidden="true">›</span
-			>
-		</a>
 	{/each}
 
 	{#if canWrite}