feat(attachments): refactor attachment management to use attachable pivot table and update related models and tests

database/migrations/2026_06_25_000600_refactor_attachments_to_attachable_pivot.php

@@ -0,0 +1,43 @@
+<?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::table('attachments', function (Blueprint $table): void {
+            $table->dropIndex(['attachable_type', 'attachable_id']);
+            $table->dropColumn(['attachable_type', 'attachable_id']);
+        });
+
+        Schema::create('attachable_attachments', function (Blueprint $table): void {
+            $table->id();
+            $table->string('attachable_type');
+            $table->unsignedBigInteger('attachable_id');
+            $table->foreignId('attachment_id')->constrained('attachments')->cascadeOnDelete();
+
+            $table->unique(['attachable_type', 'attachable_id', 'attachment_id'], 'attachable_attachments_unique');
+            $table->index(['attachable_type', 'attachable_id'], 'attachable_attachments_attachable_index');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('attachable_attachments');
+
+        Schema::table('attachments', function (Blueprint $table): void {
+            $table->string('attachable_type');
+            $table->unsignedBigInteger('attachable_id');
+            $table->index(['attachable_type', 'attachable_id']);
+        });
+    }
+};