修复登录报错提示内容错误，增加节假日同步功能

server/db.js

@@ -184,6 +184,14 @@ async function initDB() {
     )
   `);
 
+  db.run(`
+    CREATE TABLE IF NOT EXISTS holiday_cache (
+      year INTEGER PRIMARY KEY,
+      holiday_data TEXT NOT NULL,
+      updated_at TEXT NOT NULL DEFAULT (datetime('now', 'localtime'))
+    )
+  `);
+
   // Create indexes (ignore if exists)
   try { db.run("CREATE INDEX idx_timesheets_user ON timesheets(user_id)"); } catch (e) { }
   try { db.run("CREATE INDEX idx_timesheets_client ON timesheets(client_id)"); } catch (e) { }