feat: plugin scaffold with dependency check

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

src/Dependencies.php

@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP;
+
+/**
+ * Checks that the libraries WP-LIT-MCP builds on are loadable.
+ */
+final class Dependencies
+{
+    private const REQUIRED = [
+        'wordpress/mcp-adapter' => 'WP\\MCP\\Core\\McpAdapter',
+        'wp-media/mcp-oauth' => 'WPMedia\\MCP\\OAuth\\Bootstrap',
+        'WordPress Abilities API' => 'WP_Ability',
+    ];
+
+    /** @var callable(string): bool */
+    private $classExists;
+
+    public function __construct(?callable $classExists = null)
+    {
+        $this->classExists = $classExists ?? static fn (string $class): bool => class_exists($class);
+    }
+
+    /**
+     * @return list<string> Human-readable names of missing components.
+     */
+    public function missing(): array
+    {
+        $missing = [];
+        foreach (self::REQUIRED as $name => $class) {
+            if (! ($this->classExists)($class)) {
+                $missing[] = $name;
+            }
+        }
+
+        return $missing;
+    }
+}