Add FastAPI backend with agent system

backend/app/schemas/document.py

@@ -0,0 +1,40 @@
+from pydantic import BaseModel
+from datetime import datetime
+
+
+class DocumentOut(BaseModel):
+    id: str
+    title: str
+    filename: str
+    file_type: str
+    file_size: int
+    summary: str | None
+    chunk_count: int
+    is_indexed: bool
+    created_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class DocumentChunkOut(BaseModel):
+    id: str
+    chunk_index: int
+    content: str
+    metadata_: str | None
+
+    model_config = {"from_attributes": True}
+
+
+class SearchRequest(BaseModel):
+    query: str
+    top_k: int = 5
+    user_id: str
+
+
+class SearchResult(BaseModel):
+    chunk_id: str
+    document_id: str
+    document_title: str
+    content: str
+    score: float
+    metadata_: str | None