Drop the unused notes.shorturl column

The short domain is gone and nothing reads or writes this column any more.

Refs #148

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

database/migrations/2026_11_01_120000_drop_shorturl_from_notes_table.php

@@ -0,0 +1,28 @@
+<?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('notes', function (Blueprint $table) {
+            $table->dropColumn('shorturl');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('notes', function (Blueprint $table) {
+            $table->string('shorturl', 20)->nullable();
+        });
+    }
+};