feat(backend): add GET /health test to diagnostics suite

- Validates standard health response shape: status, service, version, timestamp
- Ensures consistent health endpoint contract across ecosystem

backend/src/diagnostics.test.ts

@@ -22,6 +22,13 @@ beforeAll(async () => {
     telemetryEnabled: config.TELEMETRY_ENABLED,
     featureFlagsEnabled: config.FEATURE_FLAGS_ENABLED,
   }));
+  app.get('/health', async (req) => ({
+    status: 'ok',
+    service: config.SERVICE_NAME,
+    version: '0.1.0',
+    timestamp: new Date().toISOString(),
+    requestId: req.id,
+  }));
   await app.ready();
 });
 
@@ -66,4 +73,15 @@ describe('diagnostics routes', () => {
     expect(typeof body.telemetryEnabled).toBe('boolean');
     expect(typeof body.featureFlagsEnabled).toBe('boolean');
   });
+
+  it('GET /health returns standard health response', async () => {
+    const res = await app.inject({ method: 'GET', url: '/health' });
+    expect(res.statusCode).toBe(200);
+    const body = res.json();
+    expect(body.status).toBe('ok');
+    expect(body).toHaveProperty('service');
+    expect(body).toHaveProperty('version');
+    expect(body).toHaveProperty('timestamp');
+    expect(body.timestamp).toMatch(/^\d{4}-\d{2}-\d{2}T/);
+  });
 });