refactor(briefwechsel): TagChipList defaults max to 3

Makes `max` an optional prop with default 3 — the common row-layout
case doesn't need to name the cap explicitly. ThumbnailRow's callsite
drops to `<TagChipList tags={doc.tags ?? []} />`, consistent with how
other shared components in $lib/components expose sensible defaults.

Refs #305
Fixes @leonievoss round-2 follow-up from PR review

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

frontend/src/lib/components/TagChipList.svelte

@@ -1,7 +1,7 @@
 <script lang="ts">
 type Tag = { id: string; name: string };
 
-let { tags, max }: { tags: Tag[]; max: number } = $props();
+let { tags, max = 3 }: { tags: Tag[]; max?: number } = $props();
 
 const displayedTags = $derived(tags.slice(0, max));
 const hiddenTagCount = $derived(Math.max(0, tags.length - max));

frontend/src/lib/components/TagChipList.svelte.spec.ts

@@ -31,4 +31,11 @@ describe('TagChipList', () => {
 		expect(chips).toHaveLength(0);
 		expect(document.body.textContent).not.toMatch(/\+/);
 	});
+
+	it('defaults max to 3 when the prop is omitted', () => {
+		render(TagChipList, { tags: makeTags(5) });
+		const chips = document.querySelectorAll('[data-testid="thumb-row-tag"]');
+		expect(chips).toHaveLength(3);
+		expect(document.body.textContent).toMatch(/\+2/);
+	});
 });

frontend/src/lib/components/ThumbnailRow.svelte

@@ -91,6 +91,6 @@ const ariaLabel = $derived(
 			{/if}
 		</div>
 
-		<TagChipList tags={doc.tags ?? []} max={3} />
+		<TagChipList tags={doc.tags ?? []} />
 	</div>
 </a>