diff --git a/app/main.py b/app/main.py
index e69de29..ed51cae 100644
--- a/app/main.py
+++ b/app/main.py
@@ -0,0 +1,103 @@
+import uuid
+import boto3
+from fastapi import FastAPI, HTTPException, Depends
+from sqlalchemy import create_engine, Column, String, ForeignKey
+from sqlalchemy.orm import sessionmaker, Session, declarative_base, relationship
+
+from app.config import settings
+
+# --- 数据库初始化 ---
+engine = create_engine(settings.database_url)
+SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
+Base = declarative_base()
+
+# --- S3 客户端初始化 ---
+s3_client = boto3.client(
+    's3',
+    aws_access_key_id=settings.s3_access_key,
+    aws_secret_access_key=settings.s3_secret_key,
+    endpoint_url=settings.s3_endpoint,
+    region_name=settings.s3_region
+)
+
+# --- 数据模型 ---
+class Project(Base):
+    __tablename__ = "projects"
+    id = Column(String, primary_key=True, default=lambda: str(uuid.uuid4()))
+    name = Column(String, nullable=False)
+    # cascade="all, delete-orphan" 确保在 db.delete(project) 时自动删除关联的 Markdown 记录
+    markdowns = relationship("Markdown", back_populates="project", cascade="all, delete-orphan")
+
+class Markdown(Base):
+    __tablename__ = "markdowns"
+    id = Column(String, primary_key=True, default=lambda: str(uuid.uuid4()))
+    title = Column(String, nullable=False)
+    s3_key = Column(String, nullable=False)
+    project_id = Column(String, ForeignKey("projects.id", ondelete="CASCADE"))
+    project = relationship("Project", back_populates="markdowns")
+
+Base.metadata.create_all(bind=engine)
+
+app = FastAPI()
+
+def get_db():
+    db = SessionLocal()
+    try:
+        yield db
+    finally:
+        db.close()
+
+# --- API 接口 ---
+
+@app.get("/health")
+def health():
+    return {"status": "ok"}
+
+@app.post("/projects")
+def create_project(name: str, db: Session = Depends(get_db)):
+    project = Project(name=name)
+    db.add(project)
+    db.commit()
+    db.refresh(project)
+    return project
+
+@app.post("/projects/{project_id}/markdowns")
+def upload_markdown(project_id: str, title: str, content: str, db: Session = Depends(get_db)):
+    project = db.query(Project).filter(Project.id == project_id).first()
+    if not project:
+        raise HTTPException(status_code=404, detail="Project not found")
+    
+    # 1. 存入 S3
+    s3_key = f"projects/{project_id}/{uuid.uuid4()}.md"
+    s3_client.put_object(
+        Bucket=settings.s3_bucket_name,
+        Key=s3_key,
+        Body=content,
+        ContentType="text/markdown"
+    )
+
+    # 2. 存入数据库
+    md_record = Markdown(title=title, s3_key=s3_key, project_id=project_id)
+    db.add(md_record)
+    db.commit()
+    return {"id": md_record.id, "s3_key": s3_key}
+
+@app.delete("/projects/{project_id}")
+def delete_project(project_id: str, db: Session = Depends(get_db)):
+    project = db.query(Project).filter(Project.id == project_id).first()
+    if not project:
+        raise HTTPException(status_code=404, detail="Project not found")
+    
+    # 1. 清理 S3 中的文件
+    markdowns = db.query(Markdown).filter(Markdown.project_id == project_id).all()
+    if markdowns:
+        keys = [{'Key': md.s3_key} for md in markdowns]
+        s3_client.delete_objects(
+            Bucket=settings.s3_bucket_name,
+            Delete={'Objects': keys}
+        )
+    
+    # 2. 从数据库删除项目 (SQLAlchemy 会自动处理 markdowns 表的级联删除)
+    db.delete(project)
+    db.commit()
+    return {"message": f"Project {project_id} and its files have been purged."}
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