feat(v5): authorize creates, deep-link selection, list apps in v4

Restrict V5 application and resource-connection creation to team admins.
Resolve project, environment, and application from query params and keep
session selection in sync. Surface V5 apps on the v4 resource index and
count them for project/environment emptiness. Create the flux data dir
on install and upgrade.

app/Http/Controllers/V5/ApplicationController.php

@@ -51,6 +51,7 @@ class ApplicationController extends Controller
     public function store(Request $request): JsonResponse
     {
         $currentTeam = $this->currentTeamOrFail($request);
+        $this->authorize('create', [V5Application::class, $currentTeam]);
         $projects = $this->projects($currentTeam);
         [$selectedProject, $selectedEnvironment] = $this->selectedProjectAndEnvironment($request, $projects);