feat(#221): render tag list hierarchically with indentation and color dots

TagsListPanel now accepts optional parentId/color on each Tag. A
$derived.by walk produces an ordered flat list with depth annotations.
Child tags are indented with pl-5; root-level tags with a color get
a colored dot before their name.

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

frontend/src/routes/admin/tags/TagsListPanel.svelte

@@ -1,12 +1,17 @@
 <script lang="ts">
 import { page } from '$app/state';
+import { SvelteMap } from 'svelte/reactivity';
 import { m } from '$lib/paraglide/messages.js';
 
 type Tag = {
 	id: string;
 	name: string;
+	parentId?: string;
+	color?: string;
 };
 
+type TagWithDepth = Tag & { depth: number };
+
 let {
 	tags,
 	autocollapse = false
@@ -15,6 +20,31 @@ let {
 	autocollapse?: boolean;
 } = $props();
 
+const orderedTags = $derived.by((): TagWithDepth[] => {
+	const roots = tags.filter((t) => !t.parentId);
+	const byParent = new SvelteMap<string, Tag[]>();
+	for (const t of tags) {
+		if (t.parentId) {
+			const arr = byParent.get(t.parentId) ?? [];
+			arr.push(t);
+			byParent.set(t.parentId, arr);
+		}
+	}
+	const result: TagWithDepth[] = [];
+	function walk(node: Tag, depth: number) {
+		result.push({ ...node, depth });
+		for (const child of byParent.get(node.id) ?? []) {
+			walk(child, depth + 1);
+		}
+	}
+	for (const root of roots) walk(root, 0);
+	// Append orphan children (parent not in list)
+	for (const t of tags) {
+		if (!result.find((r) => r.id === t.id)) result.push({ ...t, depth: 0 });
+	}
+	return result;
+});
+
 let manualCollapse = $state(
 	typeof localStorage !== 'undefined' &&
 		localStorage.getItem('admin_tags_list_collapsed') === 'true'
@@ -68,16 +98,26 @@ $effect(() => {
 					{m.admin_tags_empty()}
 				</p>
 			{:else}
-				{#each tags as tag (tag.id)}
+				{#each orderedTags as tag (tag.id)}
 					{@const isActive = page.url.pathname.startsWith('/admin/tags/' + tag.id)}
 					<a
 						href="/admin/tags/{tag.id}"
 						aria-current={isActive ? 'page' : undefined}
 						class="block border-l-2 px-3 py-2.5 transition-colors {isActive
 							? 'border-primary bg-primary/10 dark:bg-primary/15'
-							: 'border-transparent hover:bg-muted'}"
+							: 'border-transparent hover:bg-muted'} {tag.depth > 0 ? 'pl-5' : ''}"
 					>
-						<div class="text-sm font-bold text-ink">{tag.name}</div>
+						<div class="flex items-center text-sm font-bold text-ink">
+							{#if tag.color}
+								<span
+									data-testid="tag-list-color-dot"
+									data-color={tag.color}
+									style="background-color: var(--c-tag-{tag.color})"
+									class="mr-1.5 inline-block h-2 w-2 flex-shrink-0 rounded-full"
+								></span>
+							{/if}
+							{tag.name}
+						</div>
 					</a>
 				{/each}
 			{/if}

frontend/src/routes/admin/tags/layout.svelte.spec.ts

@@ -60,6 +60,49 @@ describe('TagsListPanel — empty state', () => {
 	});
 });
 
+// ─── Hierarchy rendering ──────────────────────────────────────────────────────
+
+describe('TagsListPanel — hierarchy', () => {
+	it('renders child tags indented under their parent', async () => {
+		render(TagsListPanel, {
+			tags: [
+				{ id: 't1', name: 'Immobilie' },
+				{ id: 't2', name: 'Haus', parentId: 't1' }
+			]
+		});
+		const childEl = document.querySelector<HTMLAnchorElement>('a[href="/admin/tags/t2"]');
+		expect(childEl?.className).toContain('pl-');
+	});
+
+	it('renders child after parent in the list', async () => {
+		render(TagsListPanel, {
+			tags: [
+				{ id: 't1', name: 'Immobilie' },
+				{ id: 't2', name: 'Haus', parentId: 't1' }
+			]
+		});
+		const links = document.querySelectorAll<HTMLAnchorElement>('a[href^="/admin/tags/t"]');
+		const hrefs = Array.from(links).map((l) => l.getAttribute('href'));
+		const parentIdx = hrefs.indexOf('/admin/tags/t1');
+		const childIdx = hrefs.indexOf('/admin/tags/t2');
+		expect(childIdx).toBeGreaterThan(parentIdx);
+	});
+
+	it('renders color dot on tags that have a color', async () => {
+		render(TagsListPanel, {
+			tags: [{ id: 't1', name: 'Immobilie', color: 'sage' }]
+		});
+		const dot = page.getByTestId('tag-list-color-dot');
+		await expect.element(dot).toBeInTheDocument();
+		await expect.element(dot).toHaveAttribute('data-color', 'sage');
+	});
+
+	it('does not render color dot on tags without a color', async () => {
+		render(TagsListPanel, { tags: [{ id: 't1', name: 'Familie' }] });
+		await expect.element(page.getByTestId('tag-list-color-dot')).not.toBeInTheDocument();
+	});
+});
+
 // ─── Collapse toggle ──────────────────────────────────────────────────────────
 
 describe('TagsListPanel — collapse toggle', () => {