Fix Alpine state reference and remove unused property in upgrade modal

- Fix incorrect Alpine state reference: Changed `this.$wire.showProgress` to `this.showProgress` in upgrade.blade.php:155
- Remove unused `$showProgress` property from Upgrade.php Livewire component
- The backend property was never set or used; all progress tracking is handled by Alpine state
- This fixes potential race conditions where the guard condition was not working as intended

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

app/Livewire/Upgrade.php

@@ -8,8 +8,6 @@
 
 class Upgrade extends Component
 {
-    public bool $showProgress = false;
-
     public bool $updateInProgress = false;
 
     public bool $isUpgradeAvailable = false;

resources/views/livewire/upgrade.blade.php

@@ -152,7 +152,7 @@ class="w-24 dark:bg-coolgray-200 dark:hover:bg-coolgray-300">Cancel
                 }, 2000);
             },
             upgrade() {
-                if (this.checkIfIamDeadInterval || this.$wire.showProgress) return true;
+                if (this.checkIfIamDeadInterval || this.showProgress) return true;
                 this.currentStatus = 'Update in progress. Pulling new images and preparing to restart Coolify...';
                 this.checkIfIamDeadInterval = setInterval(() => {
                     fetch('/api/health')