Add headless CMS for official site content management

Integrate article and page management into the Laravel admin dashboard
to serve as a headless CMS for the Next.js frontend (usher-site).

Backend:
- 7 migrations: article_categories, article_tags, articles, pivots, attachments, pages
- 5 models with relationships: Article, ArticleCategory, ArticleTag, ArticleAttachment, Page
- 4 admin controllers: articles (with publish/archive/pin), categories, tags, pages
- Admin views with EasyMDE markdown editor, multi-select categories/tags
- Navigation section "官網管理" in admin sidebar

API (v1):
- GET /api/v1/articles (filtered by type, category, tag, search; paginated)
- GET /api/v1/articles/{slug} (with related articles)
- GET /api/v1/categories
- GET /api/v1/pages/{slug} (with children)
- GET /api/v1/homepage (aggregated homepage data)
- Attachment download endpoint
- CORS configured for usher.org.tw, vercel.app, localhost:3000

Content migration:
- ImportHugoContent command: imports Hugo markdown files as articles/pages
- Successfully imported 27 articles, 17 categories, 11 tags, 9 pages

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/Http/Resources/ArticleCollectionResource.php

@@ -0,0 +1,34 @@
+<?php
+
+namespace App\Http\Resources;
+
+use Illuminate\Http\Request;
+use Illuminate\Http\Resources\Json\JsonResource;
+
+class ArticleCollectionResource extends JsonResource
+{
+    public function toArray(Request $request): array
+    {
+        return [
+            'id' => $this->id,
+            'title' => $this->title,
+            'slug' => $this->slug,
+            'summary' => $this->summary,
+            'excerpt' => $this->getExcerpt(200),
+            'content_type' => $this->content_type,
+            'content_type_label' => $this->getContentTypeLabel(),
+            'featured_image_url' => $this->featured_image_url,
+            'featured_image_alt' => $this->featured_image_alt,
+            'author_name' => $this->author_name,
+            'is_pinned' => $this->is_pinned,
+            'published_at' => $this->published_at?->toIso8601String(),
+            'categories' => CategoryResource::collection($this->whenLoaded('categories')),
+            'tags' => $this->whenLoaded('tags', function () {
+                return $this->tags->map(fn ($tag) => [
+                    'name' => $tag->name,
+                    'slug' => $tag->slug,
+                ]);
+            }),
+        ];
+    }
+}