feat: guide tool and server instructions

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

tests/Unit/Guides/InstructionsBuilderTest.php

@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace LIT\MCP\Tests\Unit\Guides;
+
+use LIT\MCP\Guides\InstructionsBuilder;
+use LIT\MCP\Integrations\Integration;
+use LIT\MCP\Integrations\IntegrationRegistry;
+use LIT\MCP\Tests\Unit\TestCase;
+use Mockery;
+
+final class InstructionsBuilderTest extends TestCase
+{
+    public function testNamesActiveIntegrationsAndCoreRules(): void
+    {
+        $core = Mockery::mock(Integration::class);
+        $core->allows('id')->andReturn('core');
+        $core->allows('isAvailable')->andReturn(true);
+
+        $text = (new InstructionsBuilder(new IntegrationRegistry($core)))->build();
+
+        self::assertStringContainsString('Aktive Integrationen: core', $text);
+        self::assertStringContainsString('lit-guide', $text);
+        self::assertStringContainsString('Status', $text);
+        self::assertLessThan(2000, strlen($text), 'Instructions must stay short – they are loaded in every conversation.');
+    }
+}