fix: add payment_method column to orders table

Migration 0008: adds payment_method column with default 'pix'
Fixes 500 error: column "payment_method" does not exist

backend/internal/repository/postgres/migrations/0008_orders_payment_method.sql

@@ -0,0 +1,7 @@
+-- Add payment_method column to orders table
+-- This column tracks how the order was paid (pix, credit_card, debit_card)
+
+ALTER TABLE orders ADD COLUMN IF NOT EXISTS payment_method TEXT NOT NULL DEFAULT 'pix';
+
+-- Add comment for documentation
+COMMENT ON COLUMN orders.payment_method IS 'Payment method: pix, credit_card, debit_card';