refactor(test): consolidate FakeApp and add sys.modules isolation utility

- Extract tests/utils/import_isolation.py with isolated_sys_modules context manager
- Extend tests/factories/app.py FakeApp with handler-specific attributes
- Refactor test_chat_handler.py to use centralized FakeApp and cached imports
- Refactor test_command_handler.py with mock_execute_factory fixture
- Refactor test_smoke.py to move import-time sys.modules manipulation into fixture
- Add SQLite migration integration tests (G-002)
- Add HTTP API smoke integration tests (G-005)
- Update CI workflow to call pytest for SQLite migrations (G-004)

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/factories/app.py

@@ -18,6 +18,8 @@ class FakeApp:
         command_prefix: list[str] = ["/", "!"],
         command_enable: bool = True,
         pipeline_concurrency: int = 10,
+        admins: list[str] | None = None,
+        **extra_attrs,
     ):
         self.logger = self._create_mock_logger()
         self.sess_mgr = self._create_mock_session_manager()
@@ -30,9 +32,19 @@ class FakeApp:
             command_prefix=command_prefix,
             command_enable=command_enable,
             pipeline_concurrency=pipeline_concurrency,
+            admins=admins or [],
         )
         self.task_mgr = self._create_mock_task_manager()
 
+        # Handler-specific optional attributes
+        self.telemetry = self._create_mock_telemetry()
+        self.survey = None
+        self.cmd_mgr = self._create_mock_cmd_mgr()
+
+        # Apply any extra attributes for specific test scenarios
+        for name, value in extra_attrs.items():
+            setattr(self, name, value)
+
         # Captured outbound messages (for assertions)
         self._outbound_messages: list = []
 
@@ -82,11 +94,13 @@ class FakeApp:
         command_prefix: list[str],
         command_enable: bool,
         pipeline_concurrency: int,
+        admins: list[str],
     ):
         instance_config = Mock()
         instance_config.data = {
             "command": {"prefix": command_prefix, "enable": command_enable},
             "concurrency": {"pipeline": pipeline_concurrency},
+            "admins": admins,
         }
         return instance_config
 
@@ -95,6 +109,16 @@ class FakeApp:
         task_mgr.create_task = Mock()
         return task_mgr
 
+    def _create_mock_telemetry(self):
+        telemetry = AsyncMock()
+        telemetry.start_send_task = AsyncMock()
+        return telemetry
+
+    def _create_mock_cmd_mgr(self):
+        cmd_mgr = AsyncMock()
+        cmd_mgr.execute = AsyncMock()
+        return cmd_mgr
+
     def capture_message(self, message):
         """Capture an outbound message for test assertions."""
         self._outbound_messages.append(message)