feat(updater): wire tauri-plugin-updater with GitHub releases endpoint + update toast

src/routes/+layout.svelte

@@ -10,6 +10,7 @@
   import { loadOsInfo } from "$lib/utils/osInfo.js";
   import { page, settings, saveSettings } from "$lib/stores/page.svelte.js";
   import { getPreferences, updatePreferences } from "$lib/stores/preferences.svelte.js";
+  import { toasts } from "$lib/stores/toasts.svelte.js";
 
   import { page as sveltePage } from "$app/stores";
 
@@ -230,6 +231,15 @@
     } catch {
       // If commands fail, skip first-run check
     }
+
+    // Background update check — non-blocking, silent on failure
+    invoke("check_for_update")
+      .then((version) => {
+        if (version) {
+          toasts.info(`Kon ${version} is available. Restart to install.`);
+        }
+      })
+      .catch(() => { /* update check failure must not affect the app */ });
   });
 
   onDestroy(() => {