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

database/migrations/2026_02_15_000002_create_account_sale_and_account_expense_tables.php

@@ -0,0 +1,36 @@
+<?php
+
+use Illuminate\Database\Migrations\Migration;
+use Illuminate\Database\Schema\Blueprint;
+use Illuminate\Support\Facades\Schema;
+
+return new class extends Migration
+{
+    public function up(): void
+    {
+        Schema::create('account_sale', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('sale_id')->constrained()->onDelete('cascade');
+            $table->foreignId('account_id')->constrained()->onDelete('cascade');
+            $table->timestamps();
+
+            $table->unique(['sale_id', 'account_id']);
+        });
+
+        Schema::create('account_expense', function (Blueprint $table) {
+            $table->id();
+            $table->foreignId('expense_id')->constrained()->onDelete('cascade');
+            $table->foreignId('account_id')->constrained()->onDelete('cascade');
+            $table->timestamps();
+
+            $table->unique(['expense_id', 'account_id']);
+        });
+    }
+
+    public function down(): void
+    {
+        Schema::dropIfExists('account_expense');
+        Schema::dropIfExists('account_sale');
+    }
+};
+