Fix account balances unique constraint

- Drop and recreate the broken unique index on account_balances table
- Ensure proper unique constraint on (account_id, balance_date)

database/migrations/2025_11_29_170955_fix_account_balances_unique_constraint.php

@@ -0,0 +1,34 @@
+<?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('account_balances', function (Blueprint $table) {
+            // Drop the broken index
+            $table->dropUnique('account_balances_account_id_balance_date_unique');
+
+            // Recreate it properly
+            $table->unique(['account_id', 'balance_date'], 'account_balances_account_id_balance_date_unique');
+        });
+    }
+
+    /**
+     * Reverse the migrations.
+     */
+    public function down(): void
+    {
+        Schema::table('account_balances', function (Blueprint $table) {
+            $table->dropUnique('account_balances_account_id_balance_date_unique');
+            // Restoration might be tricky if we don't know the exact broken state, but let's assume valid state
+            $table->unique(['account_id', 'balance_date'], 'account_balances_account_id_balance_date_unique');
+        });
+    }
+};