ALTER TABLE users ADD COLUMN notices_read_at DATETIME;

CREATE TABLE notices (
  id INTEGER PRIMARY KEY AUTOINCREMENT,
  type TEXT NOT NULL CHECK (type IN ('important','feature','news','reward','version','promo')),
  user_id INTEGER,                     -- NULL=全员广播;非空=定向该用户
  title_zh TEXT NOT NULL,
  title_en TEXT NOT NULL,
  body_zh TEXT,
  body_en TEXT,
  link TEXT,
  published_at DATETIME NOT NULL,
  expires_at DATETIME,
  revoked_at DATETIME,
  email_sent_at DATETIME,
  FOREIGN KEY (user_id) REFERENCES users(id)
);
CREATE INDEX ix_notices_user_pub ON notices(user_id, published_at);