feat(workflows): M6 — dashboard run-history + DAG view

A per-app "Workflows" tab: list definitions, browse run history, and inspect a
run's per-step progress with a static layered DAG.

- API: the run-detail endpoint now returns each step's `depends_on` (loaded
  from the definition via a new `get_workflow_by_id` reader) so the dashboard
  can draw the graph edges — the run's step rows don't carry them.
- dashboard `$lib/api`: a `workflows` namespace (list / runs / start / run) +
  the matching types.
- `apps/[slug]/workflows/+page.svelte`: workflow table → drill into runs →
  drill into a run. The run view renders a step table plus an SVG DAG (nodes =
  steps colored by status, laid out by longest-path level; edges = depends_on,
  arrowed) and a "Start run" button. Nested/parked steps show their child run.
- AppTabBar + the per-app layout gain the Workflows tab (admin-only).

Tests: `npm run check` clean (0 errors); two Playwright smoke tests
(navigation tabs — workflows loads cleanly + renders its empty state) pass
against the full stack.

With M6 the v1.2 Workflows track (M1 schema/validation → M2 durable
orchestrator → M3 when/templating → M4 nested → M5 SDK/API/CLI → M6 dashboard)
is COMPLETE.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

dashboard/tests/e2e/navigation/tabs.spec.ts

@@ -105,6 +105,7 @@ const TABS: Array<{ subpath: string; label: string }> = [
 	{ subpath: '', label: 'main' },
 	{ subpath: '/queues', label: 'queues' },
 	{ subpath: '/queues/never-enqueued', label: 'queue drilldown' },
+	{ subpath: '/workflows', label: 'workflows' },
 	{ subpath: '/files', label: 'files' },
 	{ subpath: '/dead-letters', label: 'dead-letters' },
 	{ subpath: '/users', label: 'app users' },
@@ -154,4 +155,21 @@ test.describe('per-app tab navigation accepts slug URLs', () => {
 		// DOM element.
 		await expect(page.getByTestId('queues-empty-state')).toBeVisible();
 	});
+
+	test('workflows tab renders its empty state (v1.2)', async ({ page, uniqueSlug }) => {
+		const slug = uniqueSlug('wf');
+		cleanup.app(slug);
+		const api = await adminApi();
+		try {
+			const res = await api.post('/api/v1/admin/apps', {
+				data: { slug, name: slug }
+			});
+			expect(res.ok()).toBe(true);
+		} finally {
+			await api.dispose();
+		}
+		await expectTabLoadsCleanly(page, `/admin/apps/${slug}/workflows`);
+		// A fresh app has no workflows → the empty-state anchors the smoke test.
+		await expect(page.getByTestId('workflows-empty-state')).toBeVisible();
+	});
 });