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_config_loader.py

@@ -0,0 +1,107 @@
+import json
+
+from beaver.engine import AgentLoop, EngineLoader
+from beaver.engine.providers import make_provider_bundle
+from beaver.engine.providers.litellm import LiteLLMProvider
+from beaver.foundation.config import load_config
+
+
+def test_load_config_reads_current_instance_shape(tmp_path) -> None:
+    config_path = tmp_path / "config.json"
+    config_path.write_text(
+        json.dumps(
+            {
+                "agents": {
+                    "defaults": {
+                        "workspace": str(tmp_path / "workspace"),
+                        "model": "qwen-plus",
+                    }
+                },
+                "providers": {
+                    "openai": {
+                        "apiKey": "sk-test",
+                        "apiBase": "https://oai.example.com/v1",
+                        "extraHeaders": {"X-Test": "1"},
+                    }
+                },
+                "embeddingModel": "text-embedding-v4",
+            }
+        ),
+        encoding="utf-8",
+    )
+
+    config = load_config(config_path=config_path)
+    target = config.resolve_provider_target()
+
+    assert config.default_model == "qwen-plus"
+    assert config.default_embedding_model == "text-embedding-v4"
+    assert target["provider_name"] == "openai"
+    assert target["model"] == "qwen-plus"
+    assert target["api_key"] == "sk-test"
+    assert target["api_base"] == "https://oai.example.com/v1"
+    assert target["extra_headers"] == {"X-Test": "1"}
+
+
+def test_engine_loader_uses_config_workspace(tmp_path) -> None:
+    workspace = tmp_path / "workspace"
+    config_path = tmp_path / "config.json"
+    config_path.write_text(
+        json.dumps(
+            {
+                "agents": {
+                    "defaults": {
+                        "workspace": str(workspace),
+                        "model": "qwen-plus",
+                    }
+                },
+                "providers": {"openai": {"apiKey": "sk-test", "apiBase": "https://oai.example.com/v1"}},
+            }
+        ),
+        encoding="utf-8",
+    )
+
+    loader = EngineLoader(config_path=config_path)
+    assert loader.workspace == workspace
+
+
+def test_agent_loop_config_drives_provider_bundle(tmp_path) -> None:
+    workspace = tmp_path / "workspace"
+    config_path = tmp_path / "config.json"
+    config_path.write_text(
+        json.dumps(
+            {
+                "agents": {
+                    "defaults": {
+                        "workspace": str(workspace),
+                        "model": "qwen-plus",
+                    }
+                },
+                "providers": {"openai": {"apiKey": "sk-test", "apiBase": "https://oai.example.com/v1"}},
+            }
+        ),
+        encoding="utf-8",
+    )
+
+    loop = AgentLoop(loader=EngineLoader(config_path=config_path))
+    loaded = loop.boot()
+    target = loaded.config.resolve_provider_target()
+
+    assert target["provider_name"] == "openai"
+    assert target["model"] == "qwen-plus"
+    assert target["api_key"] == "sk-test"
+    assert target["api_base"] == "https://oai.example.com/v1"
+    loop.close()
+
+
+def test_openai_compatible_qwen_config_keeps_openai_provider() -> None:
+    bundle = make_provider_bundle(
+        model="qwen-plus",
+        provider_name="openai",
+        api_key="sk-test",
+        api_base="https://oai.example.com/v1",
+    )
+
+    assert bundle.main_runtime.provider_name == "openai"
+    assert bundle.main_runtime.api_base == "https://oai.example.com/v1"
+    assert isinstance(bundle.main_provider, LiteLLMProvider)
+    assert bundle.main_provider._resolve_model("qwen-plus") == "openai/qwen-plus"