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/beaver/engine/loader.py

@@ -2,17 +2,27 @@
 
 from __future__ import annotations
 
+import os
 from dataclasses import dataclass, field
 from pathlib import Path
 from typing import Callable
 
 from beaver.engine.context import ContextBuilder
 from beaver.engine.session import SessionManager
+from beaver.foundation.config import BeaverConfig, load_config
 from beaver.memory.curated.store import MemoryStore
 from beaver.services.memory_service import MemoryService
 from beaver.skills import SkillAssembler, SkillsLoader
-from beaver.tools import ObjectBackedTool, ToolExecutor, ToolRegistry
-from beaver.tools.builtins import EchoTool, MemoryTool, SessionSearchTool, SkillViewTool
+from beaver.tools import ObjectBackedTool, ToolAssembler, ToolExecutor, ToolRegistry
+from beaver.tools.builtins import (
+    EchoTool,
+    ListDirectoryTool,
+    MemoryTool,
+    ReadFileTool,
+    SearchFilesTool,
+    SessionSearchTool,
+    SkillViewTool,
+)
 
 
 @dataclass(slots=True)
@@ -27,6 +37,7 @@ class EngineLoadResult:
     """
 
     workspace: Path
+    config: BeaverConfig = field(default_factory=BeaverConfig)
     tools: list[str] = field(default_factory=list)
     skills: list[str] = field(default_factory=list)
     memory_stores: list[str] = field(default_factory=list)
@@ -35,6 +46,7 @@ class EngineLoadResult:
     curated_memory_store: MemoryStore | None = None
     memory_service: MemoryService | None = None
     tool_registry: ToolRegistry | None = None
+    tool_assembler: ToolAssembler | None = None
     tool_executor: ToolExecutor | None = None
     context_builder: ContextBuilder | None = None
     skills_loader: SkillsLoader | None = None
@@ -89,19 +101,26 @@ class EngineLoader:
         self,
         *,
         workspace: str | Path | None = None,
+        config_path: str | Path | None = None,
+        config: BeaverConfig | None = None,
         session_manager: SessionManager | None = None,
         curated_memory_store: MemoryStore | None = None,
         memory_service: MemoryService | None = None,
         tool_registry: ToolRegistry | None = None,
+        tool_assembler: ToolAssembler | None = None,
         context_builder: ContextBuilder | None = None,
         skills_loader: SkillsLoader | None = None,
         skill_assembler: SkillAssembler | None = None,
     ) -> None:
-        self.workspace = Path(workspace or Path.cwd())
+        self.config = config or load_config(workspace=workspace, config_path=config_path)
+        configured_workspace = self.config.agents_defaults.workspace
+        env_workspace = os.getenv("BEAVER_WORKSPACE")
+        self.workspace = Path(workspace or configured_workspace or env_workspace or Path.cwd())
         self._session_manager = session_manager
         self._curated_memory_store = curated_memory_store
         self._memory_service = memory_service
         self._tool_registry = tool_registry
+        self._tool_assembler = tool_assembler
         self._context_builder = context_builder
         self._skills_loader = skills_loader
         self._skill_assembler = skill_assembler
@@ -127,15 +146,20 @@ class EngineLoader:
                     ObjectBackedTool(MemoryTool(store=memory_service.get_store())),
                     ObjectBackedTool(SkillViewTool(loader=skills_loader)),
                     ObjectBackedTool(SessionSearchTool(db=session_manager)),
+                    ObjectBackedTool(ListDirectoryTool()),
+                    ObjectBackedTool(ReadFileTool()),
+                    ObjectBackedTool(SearchFilesTool()),
                 ]
             )
 
         context_builder = self._context_builder or ContextBuilder()
+        tool_assembler = self._tool_assembler or ToolAssembler()
         tool_executor = ToolExecutor(tool_registry)
         skill_assembler = self._skill_assembler or SkillAssembler(skills_loader)
 
         result = EngineLoadResult(
             workspace=workspace,
+            config=self.config,
             tools=[spec.name for spec in tool_registry.list_specs()],
             skills=[record.name for record in skills_loader.list_skills(filter_unavailable=False)],
             memory_stores=["curated"],
@@ -144,6 +168,7 @@ class EngineLoader:
             curated_memory_store=memory_service.get_store(),
             memory_service=memory_service,
             tool_registry=tool_registry,
+            tool_assembler=tool_assembler,
             tool_executor=tool_executor,
             context_builder=context_builder,
             skills_loader=skills_loader,