修复多个问题

backend/app/database.py

@@ -1,6 +1,6 @@
 from collections.abc import Generator
 
-from sqlalchemy import create_engine
+from sqlalchemy import create_engine, inspect, text
 from sqlalchemy.orm import declarative_base, sessionmaker
 
 from app.config import settings
@@ -15,9 +15,39 @@ SessionLocal = sessionmaker(autocommit=False, autoflush=False, bind=engine)
 Base = declarative_base()
 
 
+def ensure_database_schema() -> None:
+    inspector = inspect(engine)
+    if "html_files" not in inspector.get_table_names():
+        return
+
+    existing_columns = {
+        column["name"]
+        for column in inspector.get_columns("html_files")
+    }
+    column_migrations = {
+        "title": "ALTER TABLE html_files ADD COLUMN title VARCHAR(120)",
+        "source": "ALTER TABLE html_files ADD COLUMN source VARCHAR(80)",
+        "request_id": "ALTER TABLE html_files ADD COLUMN request_id VARCHAR(120)",
+        "size_bytes": "ALTER TABLE html_files ADD COLUMN size_bytes INTEGER",
+        "expires_at": "ALTER TABLE html_files ADD COLUMN expires_at DATETIME",
+    }
+
+    with engine.begin() as connection:
+        for column_name, statement in column_migrations.items():
+            if column_name not in existing_columns:
+                connection.execute(text(statement))
+
+        connection.execute(
+            text(
+                "CREATE INDEX IF NOT EXISTS ix_html_files_expires_at "
+                "ON html_files (expires_at)"
+            )
+        )
+
+
 def get_db() -> Generator:
     db = SessionLocal()
     try:
         yield db
     finally:
-        db.close()
+        db.close()