feat(01-01): create notes table and Note model with polymorphic relationships

- Add notes migration with polymorphic columns (notable_type, notable_id)
- Add foreign key to users table for author tracking
- Add indexes on composite (notable_type, notable_id) and created_at
- Create Note model with morphTo and belongsTo relationships

database/migrations/2026_02_13_120230_create_notes_table.php

@@ -0,0 +1,31 @@
+<?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('notes', function (Blueprint $table) {
+            $table->id();
+            $table->morphs('notable'); // Creates notable_type, notable_id with composite index
+            $table->longText('content');
+            $table->foreignId('author_user_id')->constrained('users')->cascadeOnDelete();
+            $table->timestamps();
+            $table->index('created_at'); // For chronological sorting
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::dropIfExists('notes');
+    }
+};