init: 从 /root/zikai 根目录迁入

把原本散落在 /root/zikai 的 FastAPI 服务整理到 server/ 子目录，
开启独立 git 与 venv。运行时数据（config.yaml / keys / uploads）
按 .gitignore 留在工作目录但不入仓。

app/schemas/file.py

@@ -0,0 +1,35 @@
+"""文件接口 DTO。"""
+
+from __future__ import annotations
+
+from datetime import datetime
+
+from pydantic import BaseModel, Field
+
+
+class UploadedFileOut(BaseModel):
+    id: int
+    storage_path: str
+    original_filename: str
+    content_type: str
+    size_bytes: int
+    sha256: str
+    source: str
+    uploaded_by: str
+    uploaded_at: datetime
+
+    model_config = {"from_attributes": True}
+
+
+class FileUploadResponse(BaseModel):
+    id: int = Field(..., description="新写入的数据库行 ID")
+    filename: str = Field(..., description="客户端原始文件名")
+    size_bytes: int
+    sha256: str
+    storage_path: str
+    uploaded_at: datetime
+
+
+class FileListResponse(BaseModel):
+    total: int
+    items: list[UploadedFileOut]