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/Controllers/UpdateController.php

@@ -115,9 +115,13 @@ class UpdateController extends Controller
             if (!$hasMigrations) {
                 try {
                     $notificationService = new NotificationService();
+                    // For hotfixes the "to_version" is a commit SHA (e.g. "4371f17"),
+                    // not a semver string. Pass the current app version so the
+                    // notification reads "v1.1.3 has been updated" instead of "v4371f17".
+                    $notifyToVersion = ($type === 'hotfix') ? $fromVersion : $toVersion;
                     $notificationService->notifyAdminsUpgrade(
                         $fromVersion,
-                        $toVersion,
+                        $notifyToVersion,
                         0,
                         !empty($result['composer_manual_required'])
                     );