feat(app-instance): 集成Beaver后端并更新配置管理

集成新的Beaver后端服务到应用实例中，替换原有的nanobot实现。

主要变更包括：
- 在Dockerfile和环境配置中添加Beaver相关路径和配置变量
- 更新工作目录结构从.nanobot到.beaver
- 实现Beaver引擎加载器，支持配置文件加载和工具组装
- 添加内置工具如ListDirectoryTool、ReadFileTool、SearchFilesTool
- 更新消息处理流程，支持通道适配器和网关模式
- 重构技能系统，支持显式工具提示和嵌入式检索
- 改进错误处理和生命周期管理

此变更使应用实例能够使用统一的Beaver后端进行AI代理运行时管理。

app-instance/backend/tests/unit/test_imports.py

@@ -1,12 +1,13 @@
-from beaver.engine import AgentLoop
+from beaver.engine import AgentLoop, EngineLoader
 from beaver.foundation.events import InboundMessage, MessageBus, OutboundMessage
+from beaver.interfaces.channels import ChannelManager, MemoryChannelAdapter
 from beaver.interfaces.gateway.main import run_gateway
 from beaver.interfaces.web.app import create_app
 from beaver.interfaces.web.schemas import WebChatRequest, WebChatResponse
 
 
-def test_agent_loop_boots() -> None:
-    loop = AgentLoop()
+def test_agent_loop_boots(tmp_path) -> None:
+    loop = AgentLoop(loader=EngineLoader(workspace=tmp_path))
     loaded = loop.boot()
     assert "echo" in loaded.tools
     assert "memory" in loaded.tools
@@ -29,6 +30,14 @@ def test_message_bus_imports() -> None:
     assert OutboundMessage(channel="test", content="ok", session_id=None, finish_reason="stop").content == "ok"
 
 
+def test_channel_imports() -> None:
+    bus = MessageBus()
+    channel = MemoryChannelAdapter(bus)
+    manager = ChannelManager(bus)
+    manager.register(channel)
+    assert manager.channels["memory"] is channel
+
+
 def test_web_schema_imports() -> None:
     assert WebChatRequest(message="hello").message == "hello"
     assert WebChatResponse(