Add FastAPI backend with agent system

backend/app/schemas/folder.py

@@ -0,0 +1,39 @@
+from pydantic import BaseModel, Field, field_validator
+from typing import Optional, List
+from datetime import datetime
+
+class FolderCreate(BaseModel):
+    name: str = Field(..., min_length=1, max_length=255)
+    parent_id: Optional[str] = None
+
+    @field_validator('name')
+    @classmethod
+    def validate_name(cls, v):
+        forbidden = '/\\*?:'
+        for c in forbidden:
+            if c in v:
+                raise ValueError(f'Folder name cannot contain: {forbidden}')
+        return v
+
+class FolderUpdate(BaseModel):
+    name: str = Field(..., min_length=1, max_length=255)
+
+class FolderOut(BaseModel):
+    id: str
+    name: str
+    parent_id: Optional[str]
+    created_at: datetime
+    updated_at: datetime
+
+    model_config = {"from_attributes": True}
+
+class FolderTreeOut(BaseModel):
+    id: str
+    name: str
+    parent_id: Optional[str]
+    children: List["FolderTreeOut"] = []
+
+    model_config = {"from_attributes": True}
+
+# 递归模型需要 forward ref
+FolderTreeOut.model_rebuild()