feat: tick planner, delivery job, scheduler and purge

Also: test uses disabled channels instead of deleting them (FK cascade); ChannelRegistry no longer final so tests can extend it (controller ruling).

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01BCrwHHnGCB5XH968Nxokqw

core/tests/Support/FakeChannel.php

@@ -0,0 +1,32 @@
+<?php
+
+namespace Tests\Support;
+
+use App\Channels\ChannelDriver;
+use App\Channels\DeliveryOutcome;
+use App\Enums\Presence;
+use App\Models\Delivery;
+use App\Models\Event;
+use App\Models\User;
+
+final class FakeChannel implements ChannelDriver
+{
+    /** @var list<int> event ids delivered */
+    public array $delivered = [];
+
+    public function __construct(public Presence $presence = Presence::Unknown, public bool $succeed = true) {}
+
+    public function presence(User $user, array $config): Presence
+    {
+        return $this->presence;
+    }
+
+    public function deliver(Event $event, User $user, array $config, Delivery $delivery): DeliveryOutcome
+    {
+        $this->delivered[] = $event->id;
+
+        return $this->succeed ? DeliveryOutcome::ok(['n' => count($this->delivered)]) : DeliveryOutcome::failed('boom');
+    }
+
+    public function onDone(Event $event, Delivery $delivery): void {}
+}