refactor: move tag domain components to lib/tag/

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

frontend/src/lib/document/ThumbnailRow.svelte

@@ -1,6 +1,6 @@
 <script lang="ts">
 import ConversationThumbnail from '$lib/conversation/ConversationThumbnail.svelte';
-import TagChipList from '$lib/components/TagChipList.svelte';
+import TagChipList from '$lib/tag/TagChipList.svelte';
 import { formatDate } from '$lib/utils/date';
 import * as m from '$lib/paraglide/messages.js';