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>

database/migrations/2026_02_07_120006_create_pages_table.php

@@ -0,0 +1,35 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('pages', function (Blueprint $table) {
+            $table->id();
+            $table->string('title');
+            $table->string('slug')->unique();
+            $table->longText('content');
+            $table->string('template')->nullable();
+            $table->json('custom_fields')->nullable();
+            $table->string('status')->default('draft'); // draft, published
+            $table->text('meta_description')->nullable();
+            $table->json('meta_keywords')->nullable();
+            $table->foreignId('parent_id')->nullable()->constrained('pages')->nullOnDelete();
+            $table->integer('sort_order')->default(0);
+            $table->timestamp('published_at')->nullable();
+            $table->foreignId('created_by_user_id')->constrained('users')->cascadeOnDelete();
+            $table->foreignId('last_updated_by_user_id')->nullable()->constrained('users')->nullOnDelete();
+            $table->softDeletes();
+            $table->timestamps();
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('pages');
+    }
+};