Add Webhook Endpoints for external automation

- Create WebhookController with 4 endpoints:
  - POST /api/webhooks/posts - Create a new post
  - GET /api/webhooks/posts - List posts with filters
  - POST /api/webhooks/posts/{post}/publish - Trigger publishing
  - GET /api/webhooks/posts/{post}/status - Get post status
- Add X-Muninn-Token header authentication
- Add MUNINN_WEBHOOK_TOKEN config in services.php
- Add MUNINN_WEBHOOK_TOKEN to .env.example
- Add webhook routes with /webhooks prefix

All endpoints return JSON responses with success/error fields.

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

routes/api.php

@@ -3,6 +3,7 @@
 use App\Http\Controllers\Api\PostController;
 use App\Http\Controllers\Api\SiteController;
 use App\Http\Controllers\Api\SocialAccountController;
+use App\Http\Controllers\Api\WebhookController;
 use Illuminate\Support\Facades\Route;
 
 Route::get('/sites', [SiteController::class, 'index']);
@@ -12,3 +13,11 @@ Route::get('/accounts', [SocialAccountController::class, 'index']);
 Route::get('/accounts/{socialAccount}', [SocialAccountController::class, 'show']);
 
 Route::apiResource('posts', PostController::class)->names('api.posts');
+
+// Webhook endpoints (require X-Muninn-Token header)
+Route::prefix('webhooks')->group(function () {
+    Route::post('/posts', [WebhookController::class, 'createPost']);
+    Route::get('/posts', [WebhookController::class, 'listPosts']);
+    Route::post('/posts/{post}/publish', [WebhookController::class, 'publishPost']);
+    Route::get('/posts/{post}/status', [WebhookController::class, 'getPostStatus']);
+});