feat(workbench): ?app=<appId> deep-links into the active scene

After consolidating Settings into a workbench app, links from the
command menu, pill-nav, AI-tier dropdown, onboarding CTAs, and the
sub-route back-buttons had nowhere specific to go — they pointed at
`/` and dumped users at their home scene with no way to auto-open the
settings app.

- Home (+page.svelte) reads ?app=<id> on mount. If the id is a
  registered workbench app and not already in the active scene,
  addApp() it. Then scroll the carousel to that page. Strip the
  query out of history.replaceState so refresh doesn't re-open.
- Update all settings redirects (command menu, onboarding,
  AI-settings dropdown, settings/sync + settings/my-data back-links
  and breadcrumbs) to `/?app=settings`.

Unlocks: future deep-links to any app (profile, themes, spiral,
credits, …) without needing a standalone route. `?app=X&section=Y`
is the natural next step — left for when an app needs it.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/mana/apps/web/src/lib/components/layout/use-ai-tier-items.svelte.ts

@@ -184,7 +184,7 @@ export function useAiTierItems() {
 			id: 'ai-settings',
 			label: 'KI-Einstellungen',
 			icon: 'settings',
-			onClick: () => goto('/'),
+			onClick: () => goto('/?app=settings'),
 		},
 	]);
 

apps/mana/apps/web/src/lib/components/onboarding/steps/CompleteStep.svelte

@@ -84,7 +84,7 @@
 		</a>
 
 		<a
-			href="/"
+			href="/?app=settings"
 			class="p-4 rounded-xl bg-card border hover:border-primary/50 hover:shadow-md transition-all group"
 		>
 			<div class="flex items-center gap-3">

apps/mana/apps/web/src/routes/(app)/+layout.svelte

@@ -746,7 +746,7 @@
 			id: 'settings',
 			label: 'Einstellungen',
 			category: 'Navigation',
-			onExecute: () => goto('/'),
+			onExecute: () => goto('/?app=settings'),
 		},
 	];
 </script>

apps/mana/apps/web/src/routes/(app)/+page.svelte

@@ -16,6 +16,8 @@
 	import { ContextMenu, type ContextMenuItem } from '@mana/shared-ui';
 	import { Pencil, Copy, Trash, Image, Sparkle } from '@mana/shared-icons';
 	import { goto } from '$app/navigation';
+	import { page } from '$app/stores';
+	import { tick } from 'svelte';
 	import { _, locale } from 'svelte-i18n';
 	import { buildContextMenuItems, createWorkbenchContextMenu } from '$lib/context-menu';
 	import type { WorkbenchScene } from '$lib/types/workbench-scenes';
@@ -61,8 +63,24 @@
 	});
 
 	// ── Scene store wiring ──────────────────────────────────
-	onMount(() => {
-		workbenchScenesStore.initialize();
+	onMount(async () => {
+		await workbenchScenesStore.initialize();
+		// Deep-link: `/?app=settings` (or any registered appId) opens the
+		// app in the active scene (or focuses it if already open) and
+		// scrolls it into view. Used by command menu, pill-nav settings
+		// link, onboarding CTAs, sync-status banner — anywhere we used
+		// to navigate to `/settings` before the route was removed.
+		const target = $page.url.searchParams.get('app');
+		if (target && getApp(target)) {
+			const already = workbenchScenesStore.openApps.find((a) => a.appId === target);
+			if (!already) await workbenchScenesStore.addApp(target);
+			await tick();
+			scrollToPage(target);
+			// Clean the query out of the URL so refresh doesn't re-trigger.
+			const clean = new URL($page.url);
+			clean.searchParams.delete('app');
+			history.replaceState({}, '', clean);
+		}
 	});
 	onDestroy(() => {
 		workbenchScenesStore.dispose();

apps/mana/apps/web/src/routes/(app)/settings/my-data/+page.svelte

@@ -186,7 +186,7 @@
 	<div class="flex items-center justify-between gap-4">
 		<div>
 			<Breadcrumbs
-				items={[{ label: 'Home', href: '/' }, { label: 'Meine Daten' }]}
+				items={[{ label: 'Einstellungen', href: '/?app=settings' }, { label: 'Meine Daten' }]}
 			/>
 			<h1 class="text-2xl font-bold">Meine Daten</h1>
 			<p class="text-muted-foreground">

apps/mana/apps/web/src/routes/(app)/settings/sync/+page.svelte

@@ -106,7 +106,7 @@
 </script>
 
 <div>
-	<PageHeader title="Cloud Sync" backHref="/" sticky size="lg" />
+	<PageHeader title="Cloud Sync" backHref="/?app=settings" sticky size="lg" />
 
 	{#if syncBilling.loading}
 		<div class="flex items-center justify-center py-12">
@@ -268,9 +268,7 @@
 
 		<!-- Back link -->
 		<div class="mt-6">
-			<a href="/" class="text-sm text-primary hover:underline">
-				← Zurück
-			</a>
+			<a href="/?app=settings" class="text-sm text-primary hover:underline"> ← Zurück </a>
 		</div>
 	{/if}
 </div>