feat: 實作 Multi-tenancy 多租戶架構 (stancl/tenancy)

- 安裝並設定 stancl/tenancy 套件
- 分離 Central / Tenant migrations
- 建立 Tenant Model 與資料遷移指令
- 建立房東後台 CRUD (Landlord Dashboard)
- 新增租戶管理頁面 (列表、新增、編輯、詳情)
- 新增域名管理功能
- 更新部署手冊

app/Http/Controllers/Landlord/DashboardController.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\Http\Controllers\Landlord;
+
+use App\Http\Controllers\Controller;
+use App\Models\Tenant;
+use Inertia\Inertia;
+
+class DashboardController extends Controller
+{
+    public function index()
+    {
+        $stats = [
+            'totalTenants' => Tenant::count(),
+            'activeTenants' => Tenant::whereJsonContains('data->is_active', true)->count(),
+            'recentTenants' => Tenant::latest()->take(5)->get()->map(function ($tenant) {
+                return [
+                    'id' => $tenant->id,
+                    'name' => $tenant->name ?? $tenant->id,
+                    'is_active' => $tenant->is_active ?? true,
+                    'created_at' => $tenant->created_at->format('Y-m-d H:i'),
+                    'domains' => $tenant->domains->pluck('domain')->toArray(),
+                ];
+            }),
+        ];
+
+        return Inertia::render('Landlord/Dashboard', $stats);
+    }
+}