Detect cloud-only sidecar from compute devices (no sidecar rebuild needed)

Use the existing /api/compute-devices response to determine if only cloud
is available, instead of relying on the backend's is_cloud_only status field.
Hides Local (Whisper) option when the sidecar only supports cloud.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

src/lib/components/Settings.svelte

@@ -47,6 +47,9 @@
   let autoCheckUpdates = $state(true);
 
   let isCloudMode = $derived(remoteMode === "managed" || remoteMode === "byok");
+  let isCloudOnly = $derived(
+    computeDevices.length > 0 && computeDevices.every(d => d.id === "cloud")
+  );
 
   // Room creation / join state
   let shareCode = $state("");
@@ -453,7 +456,7 @@
             />
             Managed Service
           </label>
-          {#if !backendStore.isCloudOnly}
+          {#if !isCloudOnly}
           <label>
             <input
               type="radio"