M2: 主题系统（sablog经典+modern简约）+ 前台全部页面 + 老 URL 301 兼容 + markdown 双份导入

database/migrations/2026_08_11_100005_add_content_format_to_posts_table.php

@@ -0,0 +1,22 @@
+<?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::table('posts', function (Blueprint $table) {
+            $table->string('content_format', 10)->default('markdown')->after('content');
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::table('posts', function (Blueprint $table) {
+            $table->dropColumn('content_format');
+        });
+    }
+};