fix: Address PR review feedback for mock user initialization

Addresses Priority 1 and Priority 2 issues from code review:

## Priority 1 - Documentation Mismatch (FIXED)
- Removed database-management-scripts.md from this PR
- Documentation referenced wipe_database.py and restore_database.py
  which are in PR #481, not this PR
- Eliminates confusion and keeps PRs focused

## Priority 2 - Startup Logging (FIXED)
- Updated main.py to check return value of initialize_default_users()
- Uses raise_on_error=True for consistency with provider initialization
- Logs accurate success/failure status instead of unconditional message
- Follows same pattern as provider initialization (backend/main.py:153-157)

## Priority 2 - Unit Test Coverage (FIXED)
- Added 4 comprehensive unit tests for initialize_default_users():
  * test_initialize_default_users_skip_auth_true - Creates user when SKIP_AUTH=true
  * test_initialize_default_users_skip_auth_false - Skips when SKIP_AUTH=false
  * test_initialize_default_users_error_no_raise - Graceful error handling
  * test_initialize_default_users_error_with_raise - Raises when requested
- All tests pass locally (4/4)
- Patches core.mock_auth.ensure_mock_user_exists correctly

## Test Results
All new tests passing:
- test_initialize_default_users_skip_auth_true PASSED
- test_initialize_default_users_skip_auth_false PASSED
- test_initialize_default_users_error_no_raise PASSED
- test_initialize_default_users_error_with_raise PASSED

Addresses review comment: #480 (comment)

Author: manavgup

backend/main.py

@@ -150,8 +150,11 @@ async def lifespan(_app: FastAPI) -> AsyncGenerator[None, None]:
             logger.info("Initialized providers: %s", ", ".join(p.name for p in providers))
 
             # Initialize default users (mock user in development mode)
-            system_init_service.initialize_default_users()
-            logger.info("Default users initialized")
+            success = system_init_service.initialize_default_users(raise_on_error=True)
+            if success:
+                logger.info("Default users initialized successfully")
+            else:
+                logger.warning("Default users initialization skipped or failed")
         except StopIteration:
             logger.error("Failed to get database session")
             return

backend/tests/unit/test_system_initialization_service_unit.py

@@ -453,3 +453,50 @@ def test_setup_watsonx_models_error_with_raise(self, service):
             service._setup_watsonx_models(provider_id, True)
 
         assert "Model creation failed" in str(exc_info.value)
+
+    def test_initialize_default_users_skip_auth_true(self, service, mock_settings):
+        """Test initialize_default_users creates mock user when SKIP_AUTH=true."""
+        mock_settings.skip_auth = True
+        mock_user_id = uuid4()
+
+        with patch("core.mock_auth.ensure_mock_user_exists") as mock_ensure_user:
+            mock_ensure_user.return_value = mock_user_id
+
+            result = service.initialize_default_users(raise_on_error=False)
+
+            assert result is True
+            mock_ensure_user.assert_called_once_with(service.db, mock_settings)
+
+    def test_initialize_default_users_skip_auth_false(self, service, mock_settings):
+        """Test initialize_default_users skips creation when SKIP_AUTH=false."""
+        mock_settings.skip_auth = False
+
+        result = service.initialize_default_users(raise_on_error=False)
+
+        assert result is True
+        # Should not attempt to import or call ensure_mock_user_exists
+
+    def test_initialize_default_users_error_no_raise(self, service, mock_settings):
+        """Test initialize_default_users handles errors gracefully with raise_on_error=False."""
+        mock_settings.skip_auth = True
+
+        with patch("core.mock_auth.ensure_mock_user_exists") as mock_ensure_user:
+            mock_ensure_user.side_effect = Exception("User creation failed")
+
+            result = service.initialize_default_users(raise_on_error=False)
+
+            assert result is False
+            mock_ensure_user.assert_called_once()
+
+    def test_initialize_default_users_error_with_raise(self, service, mock_settings):
+        """Test initialize_default_users raises exception when raise_on_error=True."""
+        mock_settings.skip_auth = True
+
+        with patch("core.mock_auth.ensure_mock_user_exists") as mock_ensure_user:
+            mock_ensure_user.side_effect = Exception("User creation failed")
+
+            with pytest.raises(Exception) as exc_info:
+                service.initialize_default_users(raise_on_error=True)
+
+            assert "User creation failed" in str(exc_info.value)
+            mock_ensure_user.assert_called_once()