feat: add AIO sandbox provider and auto title generation (#1)

- Add AioSandboxProvider for Docker-based sandbox execution with
  configurable container lifecycle, volume mounts, and port management
- Add TitleMiddleware to auto-generate thread titles after first
  user-assistant exchange using LLM
- Add Claude Code documentation (CLAUDE.md, AGENTS.md)
- Extend SandboxConfig with Docker-specific options (image, port, mounts)
- Fix hardcoded mount path to use expanduser
- Add agent-sandbox and dotenv dependencies

Co-authored-by: Claude Opus 4.5 <noreply@anthropic.com>

backend/src/config/sandbox_config.py

@@ -1,10 +1,56 @@
-from pydantic import BaseModel, Field
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class VolumeMountConfig(BaseModel):
+    """Configuration for a volume mount."""
+
+    host_path: str = Field(..., description="Path on the host machine")
+    container_path: str = Field(..., description="Path inside the container")
+    read_only: bool = Field(default=False, description="Whether the mount is read-only")
 
 
 class SandboxConfig(BaseModel):
-    """Config section for a sandbox"""
+    """Config section for a sandbox.
+
+    Common options:
+        use: Class path of the sandbox provider (required)
+
+    AioSandboxProvider specific options:
+        image: Docker image to use (default: enterprise-public-cn-beijing.cr.volces.com/vefaas-public/all-in-one-sandbox:latest)
+        port: Base port for sandbox containers (default: 8080)
+        base_url: If set, uses existing sandbox instead of starting new container
+        auto_start: Whether to automatically start Docker container (default: true)
+        container_prefix: Prefix for container names (default: deer-flow-sandbox)
+        mounts: List of volume mounts to share directories with the container
+    """
 
     use: str = Field(
         ...,
-        description="Class path of the sandbox provider(e.g. src.sandbox.local:LocalSandbox)",
+        description="Class path of the sandbox provider (e.g. src.sandbox.local:LocalSandboxProvider)",
     )
+    image: str | None = Field(
+        default=None,
+        description="Docker image to use for the sandbox container",
+    )
+    port: int | None = Field(
+        default=None,
+        description="Base port for sandbox containers",
+    )
+    base_url: str | None = Field(
+        default=None,
+        description="If set, uses existing sandbox at this URL instead of starting new container",
+    )
+    auto_start: bool | None = Field(
+        default=None,
+        description="Whether to automatically start Docker container",
+    )
+    container_prefix: str | None = Field(
+        default=None,
+        description="Prefix for container names",
+    )
+    mounts: list[VolumeMountConfig] = Field(
+        default_factory=list,
+        description="List of volume mounts to share directories between host and container",
+    )
+
+    model_config = ConfigDict(extra="allow")