Fix update checker not detecting new versions

enable() was called before invoke("version") resolved, so the first
checkNewVersion() could run while sanitizedCurrentVersion was still
undefined. Even though newVersion is a derived value, Svelte 5 may
not reliably recompute it when state changes asynchronously on a
module-level class instance.

Moving enable() inside the invoke callback ensures sanitizedCurrentVersion
is always set before any version comparison runs.

src/lib/updateChecker.svelte.ts

@@ -58,9 +58,6 @@ class UpdateChecker {
 
   public static init(): UpdateChecker {
     const updateChecker = new UpdateChecker();
-    if (isEnabledStore.value) {
-      updateChecker.enable();
-    }
 
     void invoke<string>("version").then(currentVersion => {
       updateChecker.currentVersion = currentVersion.toString();
@@ -68,6 +65,9 @@ class UpdateChecker {
       if (version) {
         updateChecker.sanitizedCurrentVersion = version.toString();
       }
+      if (isEnabledStore.value) {
+        updateChecker.enable();
+      }
     });
 
     return updateChecker;