feat: create NAV_ADMIN user if missing; optional password sync from env

Co-authored-by: Cursor <cursoragent@cursor.com>

app.py

@@ -87,6 +87,7 @@ def create_app() -> Flask:
     with app.app_context():
         db.create_all()
         _ensure_default_user()
+        _ensure_admin_from_env()
 
     @app.route("/login", methods=["GET", "POST"])
     def login():
@@ -327,6 +328,32 @@ def _ensure_default_user() -> None:
     )
 
 
+def _ensure_admin_from_env() -> None:
+    """库中已有用户后，.env 里的管理员账号不会自动覆盖旧库；若配置了用户名且尚不存在则补建。"""
+    username = (os.environ.get("NAV_ADMIN_USERNAME") or "").strip()
+    password = os.environ.get("NAV_ADMIN_PASSWORD")
+    if not username or password is None or password == "":
+        return
+    existing = User.query.filter_by(username=username).first()
+    if existing:
+        if os.environ.get("NAV_ADMIN_UPDATE_PASSWORD") == "1":
+            existing.set_password(password)
+            db.session.commit()
+            print(
+                f"[nav] 已按 NAV_ADMIN_UPDATE_PASSWORD=1 更新用户「{username}」的登录密码。",
+                flush=True,
+            )
+        return
+    u = User(username=username)
+    u.set_password(password)
+    db.session.add(u)
+    db.session.commit()
+    print(
+        f"[nav] 已从环境变量创建用户「{username}」（此前库中无此用户名）。",
+        flush=True,
+    )
+
+
 app = create_app()
 
 if __name__ == "__main__":