fix(sources): prevent 500 when deleting GitLab/GitHub apps

After delete, Livewire still re-renders the source change view (modal
$refresh / morph). Policy @can checks then call isAdminOfTeam() with a
null team_id and throw a TypeError (HTTP 500) before the redirect.

Guard null team_id in GitlabAppPolicy and GithubAppPolicy, clear the
Livewire model after delete, and skip @can when the model is gone.

app/Livewire/Source/Github/Change.php

@@ -478,6 +478,9 @@ class Change extends Component
                 return;
             }
             $this->github_app->delete();
+            // Clear so post-delete Livewire re-render / modal $refresh does not re-run
+            // @can and canGate checks against a deleted model (null team_id TypeError).
+            $this->github_app = null;
 
             return redirect()->route('source.all');
         } catch (\Throwable $e) {