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/chunk.py

@@ -0,0 +1,46 @@
+"""
+Chunk Schemas
+"""
+from datetime import datetime
+from typing import Optional, Any
+from uuid import UUID
+from pydantic import BaseModel, ConfigDict, Field
+
+
+class ChunkBase(BaseModel):
+    """Base chunk schema"""
+    name: Optional[str] = Field(None, max_length=255)
+    content: str = Field(..., min_length=1)
+    summary: Optional[str] = None
+    word_count: Optional[int] = None
+    extra_data: Optional[dict] = None
+
+
+class ChunkCreate(ChunkBase):
+    """Chunk create schema"""
+    project_id: Optional[UUID] = None
+    file_id: Optional[UUID] = None
+
+
+class ChunkUpdate(BaseModel):
+    """Chunk update schema"""
+    name: Optional[str] = Field(None, max_length=255)
+    content: Optional[str] = Field(None, min_length=1)
+    summary: Optional[str] = None
+    extra_data: Optional[dict] = None
+
+
+class ChunkResponse(ChunkBase):
+    """Chunk response schema"""
+    model_config = ConfigDict(from_attributes=True)
+
+    id: UUID
+    project_id: UUID
+    file_id: Optional[UUID]
+    created_at: datetime
+    updated_at: datetime
+
+
+# Alias for CRUD
+ChunkCreateSchema = ChunkCreate
+ChunkUpdateSchema = ChunkUpdate