feat: add account linking and improve sales table

- Add many-to-many relationships between Sale/Expense and Account models
- Create pivot tables for account_sale and account_expense with migrations
- Implement account syncing during sale/expense creation and editing
- Add accounts_list attribute to display comma-separated account names
- Introduce SaleService with DTO for sale creation logic
- Simplify sales table columns to show branch, reference, date, and creator
- Calculate and store aggregated financial fields from transactions
- Make series field read-only instead of disabled in sale form

app/DataObjects/CreateSaleDTO.php

@@ -0,0 +1,29 @@
+<?php
+
+namespace App\DataObjects;
+
+use Carbon\Carbon;
+
+readonly class CreateSaleDTO
+{
+    /**
+     * Create a new class instance.
+     */
+    public function __construct(
+         protected string $reference_number,
+         protected Carbon $happened_on,
+         protected int $branch_id,
+         protected int $user_id,
+    )
+    {}
+
+    public function toArray(): array
+    {
+        return [
+            'reference_number' => $this->reference_number,
+            'happened_on' => $this->happened_on,
+            'branch_id' => $this->branch_id,
+            'user_id' => $this->user_id,
+        ];
+    }
+}