add CLAUDE.md and fix MQTT empty message handling

- CLAUDE.md: document project architecture, resilience constraint,
  workflow and all helper scripts
- pool.js: guard against empty MQTT messages before JSON.parse
  (prevents crash when msg is "")
- pool.js: remove stale TODO about force off when duration==0

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pool.js

@@ -299,14 +299,22 @@ MQTT.subscribe(
   function (topic, msg) {
     status.tick_mqtt++;
     print("[POOL] mqtt", topic, msg);
+<<<<<<< HEAD
     if (msg == "") {
       return;
     }
     let obj = JSON.parse(msg);
     if (obj.temperature === undefined) {
       return;
+=======
+    if (msg != "") {
+      let obj = JSON.parse(msg);
+      if (obj.temperature === undefined) {
+        return;
+      }
+      update_temp(obj.temperature);
+>>>>>>> 2d0d8cb (add CLAUDE.md and fix MQTT empty message handling)
     }
-    update_temp(obj.temperature);
   }
 )