refactor(setup): redirect to /household/staples?ctx=onboarding after household creation

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

frontend/src/routes/household/setup/+page.server.ts

@@ -34,6 +34,6 @@ export const actions = {
 			});
 		}
 
-		throw redirect(303, '/household/staples');
+		throw redirect(303, '/household/staples?ctx=onboarding');
 	}
 } satisfies Actions;

frontend/src/routes/household/setup/page.server.test.ts

@@ -97,7 +97,7 @@ describe('household setup — form action', () => {
 			expect.unreachable();
 		} catch (e: any) {
 			expect(e.status).toBe(303);
-			expect(e.location).toBe('/household/staples');
+			expect(e.location).toBe('/household/staples?ctx=onboarding');
 		}
 	});