feat(server/migrate): 000026 notices 表 + users.notices_read_at 已读水位

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01P9G7E3wmAYL9KeYCVZVsqu

server/migrations/sqlite/000026_notices.down.sql

@@ -0,0 +1,2 @@
+DROP TABLE notices;
+ALTER TABLE users DROP COLUMN notices_read_at;

server/migrations/sqlite/000026_notices.up.sql

@@ -0,0 +1,18 @@
+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);