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/ThumbnailRow.svelte

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