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/Models/Page.php

@@ -0,0 +1,130 @@
+<?php
+
+namespace App\Models;
+
+use Illuminate\Database\Eloquent\Builder;
+use Illuminate\Database\Eloquent\Factories\HasFactory;
+use Illuminate\Database\Eloquent\Model;
+use Illuminate\Database\Eloquent\SoftDeletes;
+use Illuminate\Support\Str;
+
+class Page extends Model
+{
+    use HasFactory, SoftDeletes;
+
+    const STATUS_DRAFT = 'draft';
+
+    const STATUS_PUBLISHED = 'published';
+
+    protected $fillable = [
+        'title',
+        'slug',
+        'content',
+        'template',
+        'custom_fields',
+        'status',
+        'meta_description',
+        'meta_keywords',
+        'parent_id',
+        'sort_order',
+        'published_at',
+        'created_by_user_id',
+        'last_updated_by_user_id',
+    ];
+
+    protected $casts = [
+        'custom_fields' => 'array',
+        'meta_keywords' => 'array',
+        'sort_order' => 'integer',
+        'published_at' => 'datetime',
+    ];
+
+    protected static function boot()
+    {
+        parent::boot();
+
+        static::creating(function (Page $page) {
+            if (empty($page->slug)) {
+                $slug = Str::slug($page->title);
+                if (empty($slug)) {
+                    $slug = 'page-'.time();
+                }
+                $originalSlug = $slug;
+                $count = 1;
+                while (static::withTrashed()->where('slug', $slug)->exists()) {
+                    $slug = $originalSlug.'-'.$count++;
+                }
+                $page->slug = $slug;
+            }
+        });
+    }
+
+    // ==================== Relationships ====================
+
+    public function parent()
+    {
+        return $this->belongsTo(Page::class, 'parent_id');
+    }
+
+    public function children()
+    {
+        return $this->hasMany(Page::class, 'parent_id')->orderBy('sort_order');
+    }
+
+    public function creator()
+    {
+        return $this->belongsTo(User::class, 'created_by_user_id');
+    }
+
+    public function lastUpdatedBy()
+    {
+        return $this->belongsTo(User::class, 'last_updated_by_user_id');
+    }
+
+    // ==================== Query Scopes ====================
+
+    public function scopePublished(Builder $query): Builder
+    {
+        return $query->where('status', self::STATUS_PUBLISHED);
+    }
+
+    public function scopeTopLevel(Builder $query): Builder
+    {
+        return $query->whereNull('parent_id');
+    }
+
+    // ==================== Helper Methods ====================
+
+    public function isDraft(): bool
+    {
+        return $this->status === self::STATUS_DRAFT;
+    }
+
+    public function isPublished(): bool
+    {
+        return $this->status === self::STATUS_PUBLISHED;
+    }
+
+    public function publish(?User $user = null): void
+    {
+        $updates = [
+            'status' => self::STATUS_PUBLISHED,
+            'published_at' => $this->published_at ?? now(),
+        ];
+
+        if ($user) {
+            $updates['last_updated_by_user_id'] = $user->id;
+        }
+
+        $this->update($updates);
+    }
+
+    public function getStatusLabel(): string
+    {
+        return match ($this->status) {
+            self::STATUS_DRAFT => '草稿',
+            self::STATUS_PUBLISHED => '已發布',
+            default => '未知',
+        };
+    }
+}