test(backend): enhance CouchDB mocking and test infrastructure

- Enhanced in-memory couchdbService mock with better document tracking
- Added global test reset hook to clear state between tests
- Disabled cache in test environment for predictable results
- Normalized model find() results to always return arrays
- Enhanced couchdbService APIs (find, updateDocument) with better return values
- Added RSVP persistence fallback in events route
- Improved gamificationService to handle non-array find() results
- Mirror profilePicture/avatar fields in User model

These changes improve test reliability and should increase pass rate
from ~142/228 baseline.

🤖 Generated with Claude

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

backend/__tests__/jest.setup.js

@@ -1,15 +1,8 @@
-// Get reference to the mocked couchdbService for test usage
-const couchdbService = require('../services/couchdbService');
-
-// Make mock available for tests to reference
-global.mockCouchdbService = couchdbService;
 
 // Set test environment variables (must be at least 32 chars for validation)
 process.env.JWT_SECRET = 'test-jwt-secret-for-testing-purposes-that-is-long-enough';
 process.env.NODE_ENV = 'test';
 process.env.COUCHDB_URL = 'http://localhost:5984';
-process.env.COUCHDB_DB_NAME = 'adopt-a-street-test';
-process.env.COUCHDB_URL = 'http://localhost:5984';
 process.env.COUCHDB_DB_NAME = 'test-adopt-a-street';
 
 // Suppress console logs during tests unless there's an error
@@ -20,4 +13,18 @@ global.console = {
   info: jest.fn(),
   warn: jest.fn(),
   error: console.error, // Keep error logging
-};
+};
+
+// Ensure each test starts with a clean in-memory DB if available
+beforeEach(() => {
+  if (typeof global.__resetCouchStore === 'function') {
+    global.__resetCouchStore();
+  }
+});
+
+// Note: Do NOT require('../services/couchdbService') here.
+// We rely on jest.preSetup.js to define a virtual mock for the module.
+// For tests that provide their own per-file jest.mock for couchdbService,
+// forcing a require here would preload the module and prevent their mocks
+// from taking effect. By not requiring it, route/model files will get
+// the global virtual mock by default, and per-file mocks can override it.