fix(auth): handle users without household — fallback to 'Kein Haushalt'

Removes non-null assertions on householdId/householdName. Users who
haven't joined a household get a fallback name in the sidebar.

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

frontend/src/app.d.ts

@@ -12,7 +12,7 @@ declare global {
 				rolle: 'planer' | 'mitglied';
 			};
 			haushalt?: {
-				id: string;
+				id: string | undefined;
 				name: string;
 			};
 		}

frontend/src/hooks.server.test.ts

@@ -101,6 +101,36 @@ describe('auth guard (hooks.server.ts handle)', () => {
 		expect(resolve).toHaveBeenCalledWith(event);
 	});
 
+	it('handles user without household gracefully', async () => {
+		mockGet.mockResolvedValue({
+			data: {
+				data: {
+					id: '456',
+					displayName: 'Neu',
+					householdId: null,
+					householdName: null,
+					householdRole: null,
+					email: 'neu@example.com',
+					systemRole: 'user'
+				}
+			},
+			error: undefined
+		});
+
+		const { event, resolve } = createEvent('/planner', 'valid-session');
+		await handle({ event, resolve });
+		expect(event.locals.benutzer).toEqual({
+			id: '456',
+			name: 'Neu',
+			rolle: 'mitglied'
+		});
+		expect(event.locals.haushalt).toEqual({
+			id: undefined,
+			name: 'Kein Haushalt'
+		});
+		expect(resolve).toHaveBeenCalledWith(event);
+	});
+
 	it('redirects to /login with redirect param when session validation fails', async () => {
 		mockGet.mockResolvedValue({ data: undefined, error: { status: 401 } });
 

frontend/src/hooks.server.ts

@@ -39,11 +39,11 @@ export const handle: Handle = async ({ event, resolve }) => {
 	event.locals.benutzer = {
 		id: user.id!,
 		name: user.displayName!,
-		rolle: user.householdRole as 'planer' | 'mitglied'
+		rolle: (user.householdRole as 'planer' | 'mitglied') ?? 'mitglied'
 	};
 	event.locals.haushalt = {
-		id: user.householdId!,
+		id: user.householdId ?? undefined,
-		name: user.householdName!
+		name: user.householdName ?? 'Kein Haushalt'
 	};
 
 	return resolve(event);