Fix spinner appearing every 5 secds

Provider/frontend/src/App.svelte

@@ -74,8 +74,12 @@
     return timestamp < Date.now() / 1000;
   }
 
-  async function fetchAll() {
+  let isFetching = false;
+  async function fetchAll(silent = false) {
+    if (isFetching) return;
+    isFetching = true;
     try {
+      if (!silent) status = "loading";
       const [sys, ota, upcoming] = await Promise.all([
         getSystemInfo(),
         getOTAStatus(),
@@ -91,6 +95,8 @@
         status = "error";
         errorMsg = e.message || "Connection failed";
       }
+    } finally {
+      isFetching = false;
     }
   }
 
@@ -107,8 +113,8 @@
 
   $effect(() => {
     fetchAll();
-    // Poll for status updates every 5 seconds
-    const interval = setInterval(fetchAll, 5000);
+    // Poll for status updates every 5 seconds (silently to avoid flashing)
+    const interval = setInterval(() => fetchAll(true), 5000);
     return () => clearInterval(interval);
   });