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

database/migrations/0001_01_01_000001_create_cache_table.php

@@ -1,35 +0,0 @@
-<?php
-
-use Illuminate\Database\Migrations\Migration;
-use Illuminate\Database\Schema\Blueprint;
-use Illuminate\Support\Facades\Schema;
-
-return new class extends Migration
-{
-    /**
-     * Run the migrations.
-     */
-    public function up(): void
-    {
-        Schema::create('cache', function (Blueprint $table) {
-            $table->string('key')->primary();
-            $table->mediumText('value');
-            $table->integer('expiration');
-        });
-
-        Schema::create('cache_locks', function (Blueprint $table) {
-            $table->string('key')->primary();
-            $table->string('owner');
-            $table->integer('expiration');
-        });
-    }
-
-    /**
-     * Reverse the migrations.
-     */
-    public function down(): void
-    {
-        Schema::dropIfExists('cache');
-        Schema::dropIfExists('cache_locks');
-    }
-};