test(v1): stub eventTypeService in events.create suite + cover unknown-type 400

The catalog-backed event_type validator (#800) makes a db('event_types')
lookup before the handler runs, which consumed the first queued mock
chain and shifted the pinned db() call sequence — 5 tests failed on CI.
Stub isValidEventType to true (validation isn't this suite's subject)
and add an explicit test for the new 400-on-unknown-type path.

backend/src/routes/v1/__tests__/events.create.test.js

@@ -80,7 +80,16 @@ jest.mock('../../../services/webhookService', () => ({
   buildEventSubject: jest.fn().mockReturnValue({}),
 }));
 
+// event_type is validated against the live event_types catalog (#800) —
+// that lookup would consume the first queued db() chain and shift the
+// call sequence these tests pin. Stub it valid; the invalid path has its
+// own test below.
+jest.mock('../../../services/eventTypeService', () => ({
+  isValidEventType: jest.fn().mockResolvedValue(true),
+}));
+
 const { db } = require('../../../database/db');
+const { isValidEventType } = require('../../../services/eventTypeService');
 const eventsRouter = require('../events');
 
 const buildApp = () => {
@@ -231,4 +240,16 @@ describe('v1 POST /events — issue #550 (color_theme + feedback row)', () => {
       .send({ ...BASE_BODY, feedback_enabled: 'maybe' })
       .expect(400);
   });
+
+  it('rejects an event_type unknown to the catalog with 400 (#800)', async () => {
+    isValidEventType.mockResolvedValueOnce(false);
+    const res = await request(buildApp())
+      .post('/events')
+      .send({ ...BASE_BODY, event_type: 'nope' })
+      .expect(400);
+
+    expect(isValidEventType).toHaveBeenCalledWith('nope');
+    expect(JSON.stringify(res.body.errors)).toContain('event_type');
+    expect(db).not.toHaveBeenCalled();
+  });
 });