refactor: add rector to enforce type declarations, code quality + style and remove dead code

- update CI process to include quality stage (tests + code review)
- add captainhook to install git pre-commit & pre-push hooks
- remove .devcontainer Dockerfile to use project's docker-compose services: all
services can now be started automatically using vscode
- update docs/setup-development.md

app/Libraries/ActivityPub/Controllers/SchedulerController.php

@@ -12,9 +12,12 @@ use CodeIgniter\Controller;
 
 class SchedulerController extends Controller
 {
+    /**
+     * @var string[]
+     */
     protected $helpers = ['activitypub'];
 
-    public function activity()
+    public function activity(): void
     {
         // retrieve scheduled activities from database
         $scheduledActivities = model('ActivityModel')->getScheduledActivities();
@@ -24,7 +27,7 @@ class SchedulerController extends Controller
             // send activity to all actor followers
             send_activity_to_followers(
                 $scheduledActivity->actor,
-                json_encode($scheduledActivity->payload),
+                json_encode($scheduledActivity->payload, JSON_THROW_ON_ERROR),
             );
 
             // set activity status to delivered