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/Abilities/Ability.php

@@ -0,0 +1,38 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Abilities;
+
+use WP_Error;
+
+/**
+ * One capability of the MCP server, registered with the WordPress Abilities API.
+ */
+interface Ability
+{
+    /** Ability name, e.g. "lit/guide". */
+    public function name(): string;
+
+    public function label(): string;
+
+    public function description(): string;
+
+    /** @return array<string, mixed> JSON Schema of the input. */
+    public function inputSchema(): array;
+
+    /** @return array<string, mixed>|null JSON Schema of the output, null for image results. */
+    public function outputSchema(): ?array;
+
+    /** @return array{readonly?: bool, destructive?: bool, idempotent?: bool} */
+    public function annotations(): array;
+
+    /** Whether the ability is listed as its own MCP tool (otherwise only via meta-tools). */
+    public function isDirect(): bool;
+
+    /** @param array<string, mixed> $input */
+    public function permission(array $input): bool|WP_Error;
+
+    /** @param array<string, mixed> $input */
+    public function execute(array $input): mixed;
+}