feat: simplify OTA updates with timestamp

server/routes/api.js

@@ -189,6 +189,9 @@ router.put('/config', async (req, res) => {
     if (typeof incoming.force_update === 'boolean') {
       cfg.force_update = incoming.force_update;
     }
+    if (incoming.update_timestamp) {
+      cfg.update_timestamp = incoming.update_timestamp;
+    }
     await DataService.saveConfig(cfg);
     appendReqLog(req, { category: 'admin', type: 'update_config_generic', detail: incoming });
     io.emit('config:updated', cfg);

server/routes/public.js

@@ -229,7 +229,8 @@ router.get('/config', (req, res) => {
     res.json({
         promotion: { name: cfg.promotion?.name || '', discount: cfg.promotion?.discount ?? 1 },
         lua_versions: cfg.lua_versions || {},
-        force_update: cfg.force_update === true
+        force_update: cfg.force_update === true,
+        update_timestamp: cfg.update_timestamp || 0
     });
 });