feat: make roast planner mobile PWA ready

public/js/main.js

@@ -494,6 +494,27 @@ function wireToolbar() {
   });
 }
 
+function wirePwa() {
+  const status = document.getElementById("connection-status");
+  const renderConnection = () => {
+    const offline = !navigator.onLine;
+    status.classList.toggle("hidden", !offline);
+    status.textContent = offline ? "Offline — changes continue saving on this device." : "";
+  };
+
+  window.addEventListener("online", renderConnection);
+  window.addEventListener("offline", renderConnection);
+  renderConnection();
+
+  if ("serviceWorker" in navigator) {
+    window.addEventListener("load", () => {
+      navigator.serviceWorker.register("/sw.js").catch((error) => {
+        console.warn("Service worker registration failed:", error);
+      });
+    });
+  }
+}
+
 function wireSectionNav() {
   const links = [...document.querySelectorAll(".section-nav a")];
   const sections = links
@@ -523,6 +544,7 @@ function init() {
   wireForm();
   wireDrawers();
   wireToolbar();
+  wirePwa();
   wireSectionNav();
   initPrefillPanel({ state, renderBlendRows: renderBlend, renderActuatorRows: renderActuators, renderFormFromPlan, recompute });
   initAlogPanel({ state, recompute });