feat: ability and integration infrastructure

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01At3V6SjwbMe6eMzVGW3Hs7

src/Integrations/Integration.php

@@ -0,0 +1,20 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Integrations;
+
+use LIT\MCP\Abilities\Ability;
+
+/**
+ * A group of abilities that is only registered when its theme/plugin is active.
+ */
+interface Integration
+{
+    public function id(): string;
+
+    public function isAvailable(): bool;
+
+    /** @return list<Ability> */
+    public function abilities(): array;
+}