feat(backend): 添加 API Schemas 定义

- 添加 Chunk 数据结构 (chunk.py)
- 添加 Dataset Schema (dataset.py)
- 添加 Evaluation Schema (eval.py)
- 添加 File Schema (file.py)
- 添加 Project Schema (project.py)
- 添加 Question Schema (question.py)

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

backend/app/schemas/file.py

@@ -0,0 +1,43 @@
+"""
+File Schemas
+"""
+from datetime import datetime
+from typing import Optional
+from uuid import UUID
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class FileBase(BaseModel):
+    """Base file schema"""
+    filename: str = Field(..., min_length=1, max_length=255)
+    file_type: str = Field(..., max_length=50)
+    size: Optional[int] = None
+
+
+class FileCreate(FileBase):
+    """File create schema"""
+    project_id: UUID
+    file_path: Optional[str] = None
+    status: str = "pending"
+
+
+class FileUpdate(BaseModel):
+    """File update schema"""
+    status: Optional[str] = None
+
+
+class FileResponse(FileBase):
+    """File response schema"""
+    model_config = ConfigDict(from_attributes=True)
+
+    id: UUID
+    project_id: UUID
+    file_path: Optional[str]
+    status: str
+    created_at: datetime
+    updated_at: datetime
+
+
+# Alias for CRUD
+FileCreateSchema = FileCreate
+FileUpdateSchema = FileUpdate