refactor: packet-based IPC with core/ui separation

- All logic in core layer (BackendServer runs independently)
- Packet protocol: {id, type, body} for all communications
- UI simplified: just input→backend→display
- Config, history, tools all handled by core
- BackendServer can run standalone without UI

tests/test_ui.py

@@ -10,28 +10,15 @@ class TestUIImport:
         from ui import GraphMemoryApp
         assert GraphMemoryApp is not None
 
-    def test_import_config(self):
-        from ui import AppConfig
-        assert AppConfig is not None
-
 
 class TestUIApp:
-    def test_create_app(self):
+    def test_create_app_without_backend(self):
         from ui import GraphMemoryApp
         app = GraphMemoryApp()
         assert app is not None
         assert app._backend_server is None
         assert app._backend_client is None
 
-    def test_create_app_with_config(self):
-        from ui import GraphMemoryApp, AppConfig
-        
-        config = AppConfig(api_key="test-key", base_url="https://api.test.com")
-        app = GraphMemoryApp(config=config)
-        
-        assert app._config is config
-        assert app._config.api_key == "test-key"
-
     def test_create_app_with_backend(self):
         from ui import GraphMemoryApp
         from core import BackendServer
@@ -57,14 +44,26 @@ class TestUIApp:
 class TestAppConfig:
     def test_config_from_env(self):
         from ui import AppConfig
-        
         config = AppConfig.from_env()
         assert config is not None
 
     def test_config_default_values(self):
         from ui import AppConfig
-        
         config = AppConfig()
         assert config.api_key == ""
         assert config.model == "deepseek-chat"
-        assert config.base_url == "https://api.deepseek.com"
+        assert config.base_url == "https://api.deepseek.com"
+
+
+class TestPacketProtocol:
+    def test_import_packet(self):
+        from core import Packet, PacketType
+        assert Packet is not None
+        assert PacketType is not None
+
+    def test_packet_creation(self):
+        from core import Packet, PacketType
+        packet = Packet(id="test-1", type=PacketType.MESSAGE, body={"message": "hello"})
+        assert packet.id == "test-1"
+        assert packet.type == PacketType.MESSAGE
+        assert packet.body["message"] == "hello"