fix(user-deletion): handle GitHub app sources across team cleanup

Limit team cleanup to apps owned by the deleted team and nullify cross-team application source references before deleting team-owned sources. Adds feature tests covering user deletion with GitHub app-backed applications, preserving system-wide apps, and nullifying external source links.

app/Models/Team.php

@@ -76,8 +76,10 @@ class Team extends Model implements SendsDiscord, SendsEmail, SendsPushover, Sen
             foreach ($keys as $key) {
                 $key->delete();
             }
-            $sources = $team->sources();
-            foreach ($sources as $source) {
+            // Only delete sources owned by this team, not system-wide ones from other teams
+            $teamSources = GithubApp::where('team_id', $team->id)->get()
+                ->merge(GitlabApp::where('team_id', $team->id)->get());
+            foreach ($teamSources as $source) {
                 $source->delete();
             }
             $tags = Tag::whereTeamId($team->id)->get();

app/Models/User.php

@@ -176,6 +176,23 @@ class User extends Authenticatable implements SendsEmail
             $project->forceDelete();
         }
 
+        // Detach applications from other teams that reference this team's sources,
+        // so the GithubApp/GitlabApp deleting guard doesn't block team deletion
+        $githubAppIds = GithubApp::where('team_id', $team->id)->pluck('id');
+        $gitlabAppIds = GitlabApp::where('team_id', $team->id)->pluck('id');
+
+        if ($githubAppIds->isNotEmpty()) {
+            Application::where('source_type', GithubApp::class)
+                ->whereIn('source_id', $githubAppIds)
+                ->update(['source_id' => null, 'source_type' => null]);
+        }
+
+        if ($gitlabAppIds->isNotEmpty()) {
+            Application::where('source_type', GitlabApp::class)
+                ->whereIn('source_id', $gitlabAppIds)
+                ->update(['source_id' => null, 'source_type' => null]);
+        }
+
         $team->members()->detach($user->id);
         $team->delete();
     }