fix(security): no direct HTTP access to plugin PHP files (audit L2, cheap part)

Every file under src/ exits outside WordPress (defined('ABSPATH') ||
exit; after the use block, so a direct request no longer prints a fatal
error with the server path); divi-convert-fixture.php gets the WP_CLI
guard the other integration scripts have. A unit test keeps both true;
PSR1 side-effects warning excluded for the guard.

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

src/Integrations/Core/CoreIntegration.php

@@ -8,6 +8,8 @@ use LIT\MCP\Access;
 use LIT\MCP\Guides\GuideRepository;
 use LIT\MCP\Integrations\Integration;
 
+defined('ABSPATH') || exit;
+
 final class CoreIntegration implements Integration
 {
     public function __construct(private string $guidesDirectory)

src/Integrations/Core/EnvironmentProbe.php

@@ -4,6 +4,8 @@ declare(strict_types=1);
 
 namespace LIT\MCP\Integrations\Core;
 
+defined('ABSPATH') || exit;
+
 /**
  * Detects the themes/plugins LIT MCP integrates with.
  */

src/Integrations/Core/GuideAbility.php

@@ -10,6 +10,8 @@ use LIT\MCP\Abilities\Errors;
 use LIT\MCP\Guides\GuideRepository;
 use WP_Error;
 
+defined('ABSPATH') || exit;
+
 final class GuideAbility implements Ability
 {
     private const DEFAULT_TOPIC = 'overview';

src/Integrations/Core/SiteStatusAbility.php

@@ -9,6 +9,8 @@ use LIT\MCP\Abilities\Annotations;
 use LIT\MCP\Access;
 use WP_Error;
 
+defined('ABSPATH') || exit;
+
 final class SiteStatusAbility implements Ability
 {
     public function __construct(private EnvironmentProbe $probe, private Access $access)