fix: resolve uncloseable database restore modal on MariaDB import (#7335)

Fixes the "Snapshot missing on Livewire component" error that occurs when
toggling the "Backup includes all databases" checkbox during MariaDB database
import operations.

Root Cause:
- ActivityMonitor component was initialized without proper lifecycle hooks
- When parent Import component re-rendered (via checkbox toggle), the
  ActivityMonitor's Livewire snapshot became stale
- Missing null checks caused errors when querying with undefined activityId
- No state cleanup when slide-over closed, causing issues on subsequent opens

Changes:
- Add updatedActivityId() lifecycle hook to ActivityMonitor for proper hydration
- Add defensive null check in hydrateActivity() to prevent query errors
- Track activityId in Import component for state management
- Add slideOverClosed event dispatch in slide-over component
- Add event listener in Import component to reset activityId on close

Testing:
- Manually verify checkbox toggle doesn't trigger popup
- Verify actual restore operations work correctly
- Test both file-based and S3-based restore methods
- Ensure X button properly closes the modal
- Verify no console errors or Livewire warnings

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

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

app/Livewire/ActivityMonitor.php

@@ -10,7 +10,7 @@ class ActivityMonitor extends Component
 {
     public ?string $header = null;
 
-    public $activityId;
+    public $activityId = null;
 
     public $eventToDispatch = 'activityFinished';
 
@@ -49,9 +49,24 @@ class ActivityMonitor extends Component
 
     public function hydrateActivity()
     {
+        if ($this->activityId === null) {
+            $this->activity = null;
+
+            return;
+        }
+
         $this->activity = Activity::find($this->activityId);
     }
 
+    public function updatedActivityId($value)
+    {
+        if ($value) {
+            $this->hydrateActivity();
+            $this->isPollingActive = true;
+            self::$eventDispatched = false;
+        }
+    }
+
     public function polling()
     {
         $this->hydrateActivity();