Fix update notifications and clear update cache

Handle hotfix upgrade messaging and clear stale update state after applying updates.

- UpdateController: when notifying admins for hotfixes, pass the current app version as the "to" version so notifications read e.g. "v1.1.3 has been updated" instead of showing a commit SHA.
- NotificationService: adjust system upgrade message to show a simple "has been updated" message when fromVersion equals toVersion (hotfix/file updates) and standard "upgraded from X to Y" otherwise; factor migration label formatting.
- UpdateService: clear cached update-check state after a successful update (add clearUpdateCache method) so the UI no longer shows a stale "update available" card. Keep latest_available_version unchanged to avoid view inconsistencies before migrations run.

app/Services/NotificationService.php

@@ -573,7 +573,13 @@ class NotificationService
      */
     public function notifySystemUpgrade(int $userId, string $fromVersion, string $toVersion, int $migrationsCount, bool $composerManualRequired = false): void
     {
-        $message = "Domain Monitor upgraded from v{$fromVersion} to v{$toVersion} ({$migrationsCount} migration" . ($migrationsCount > 1 ? 's' : '') . " applied)";
+        $migrationLabel = $migrationsCount . ' migration' . ($migrationsCount !== 1 ? 's' : '') . ' applied';
+        if ($fromVersion === $toVersion) {
+            // Hotfix: same version, just file updates
+            $message = "Domain Monitor v{$toVersion} has been updated ({$migrationLabel})";
+        } else {
+            $message = "Domain Monitor upgraded from v{$fromVersion} to v{$toVersion} ({$migrationLabel})";
+        }
         if ($composerManualRequired) {
             $message .= ". Composer could not be run here (e.g. exec disabled). If dependencies changed, run \"composer install --no-dev\" manually via SSH or Terminal.";
         }