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_000000_create_users_table.php

@@ -1,49 +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('users', function (Blueprint $table) {
-            $table->id();
-            $table->string('name');
-            $table->string('email')->unique();
-            $table->timestamp('email_verified_at')->nullable();
-            $table->string('password');
-            $table->rememberToken();
-            $table->timestamps();
-        });
-
-        Schema::create('password_reset_tokens', function (Blueprint $table) {
-            $table->string('email')->primary();
-            $table->string('token');
-            $table->timestamp('created_at')->nullable();
-        });
-
-        Schema::create('sessions', function (Blueprint $table) {
-            $table->string('id')->primary();
-            $table->foreignId('user_id')->nullable()->index();
-            $table->string('ip_address', 45)->nullable();
-            $table->text('user_agent')->nullable();
-            $table->longText('payload');
-            $table->integer('last_activity')->index();
-        });
-    }
-
-    /**
-     * Reverse the migrations.
-     */
-    public function down(): void
-    {
-        Schema::dropIfExists('users');
-        Schema::dropIfExists('password_reset_tokens');
-        Schema::dropIfExists('sessions');
-    }
-};