feat: use xpier media library for uploads and markdown embeds

Store media:ID in post bodies instead of CDN URLs, and keep sablog attach tokens as a fallback.

Co-authored-by: Cursor <cursoragent@cursor.com>

database/migrations/2026_09_16_000001_add_cover_media_id_to_posts_and_categories.php

@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        if (! Schema::hasColumn('posts', 'cover_media_id')) {
+            Schema::table('posts', function (Blueprint $table): void {
+                $table->unsignedBigInteger('cover_media_id')->nullable()->after('keywords');
+            });
+        }
+
+        if (! Schema::hasColumn('categories', 'cover_media_id')) {
+            Schema::table('categories', function (Blueprint $table): void {
+                $table->unsignedBigInteger('cover_media_id')->nullable()->after('description');
+            });
+        }
+    }
+
+    public function down(): void
+    {
+        if (Schema::hasColumn('posts', 'cover_media_id')) {
+            Schema::table('posts', function (Blueprint $table): void {
+                $table->dropColumn('cover_media_id');
+            });
+        }
+
+        if (Schema::hasColumn('categories', 'cover_media_id')) {
+            Schema::table('categories', function (Blueprint $table): void {
+                $table->dropColumn('cover_media_id');
+            });
+        }
+    }
+};

database/migrations/2026_09_16_000002_seed_default_media_folders.php

@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Support\Facades\DB;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        if (! Schema::hasTable('media_folders')) {
+            return;
+        }
+
+        $now = now();
+        $folders = [
+            ['code' => 'general', 'name' => 'General', 'sort' => 0],
+            ['code' => 'articles', 'name' => 'Articles', 'sort' => 1],
+            ['code' => 'banners', 'name' => 'Banners', 'sort' => 2],
+        ];
+
+        foreach ($folders as $folder) {
+            $exists = DB::table('media_folders')->where('code', $folder['code'])->exists();
+            if ($exists) {
+                continue;
+            }
+
+            DB::table('media_folders')->insert([
+                'parent_id' => null,
+                'code' => $folder['code'],
+                'name' => $folder['name'],
+                'sort' => $folder['sort'],
+                'is_active' => true,
+                'created_at' => $now,
+                'updated_at' => $now,
+            ]);
+        }
+    }
+
+    public function down(): void
+    {
+        if (! Schema::hasTable('media_folders')) {
+            return;
+        }
+
+        DB::table('media_folders')
+            ->whereIn('code', ['general', 'articles', 'banners'])
+            ->whereNull('parent_id')
+            ->delete();
+    }
+};