Fix P0-P2 bugs: sale.order M2M, display_name, DefaultGet

P0: Fix sale.order creation (was completely broken)
- Corrected M2M junction table name from sale_order_line_account_tax_rel
  to account_tax_sale_order_line_rel (ORM sorts alphabetically)
- Added fallback in BeforeCreate if sequence generation fails

P1: Add display_name as magic field on ALL models
- Added to addMagicFields() in pkg/orm/model.go (like Python BaseModel)
- Computed on-the-fly in Read() from recName field, no DB column
- Removed explicit display_name from res.partner (now auto-inherited)

P2: Add DefaultGet hooks for sale.order and purchase.order
- Sets company_id, currency_id, date_order/date_planned from environment
- Follows same pattern as account.move's DefaultGet

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

addons/sale/models/sale_order.go

@@ -135,7 +135,7 @@ func initSaleOrder() {
 			`SELECT COALESCE(SUM(
 				product_uom_qty * price_unit * (1 - COALESCE(discount,0)/100)
 				* COALESCE((SELECT t.amount / 100 FROM account_tax t
-					JOIN sale_order_line_account_tax_rel rel ON rel.account_tax_id = t.id
+					JOIN account_tax_sale_order_line_rel rel ON rel.account_tax_id = t.id
 					WHERE rel.sale_order_line_id = sol.id LIMIT 1), 0)
 			), 0)
 			 FROM sale_order_line sol WHERE sol.order_id = $1
@@ -156,12 +156,41 @@ func initSaleOrder() {
 	m.RegisterCompute("amount_tax", computeSaleAmounts)
 	m.RegisterCompute("amount_total", computeSaleAmounts)
 
+	// -- DefaultGet: Provide dynamic defaults for new records --
+	// Mirrors: odoo/addons/sale/models/sale_order.py SaleOrder.default_get()
+	// Supplies company_id, currency_id, date_order when creating a new quotation.
+	m.DefaultGet = func(env *orm.Environment, fields []string) orm.Values {
+		vals := make(orm.Values)
+
+		// Default company from the current user's session
+		companyID := env.CompanyID()
+		if companyID > 0 {
+			vals["company_id"] = companyID
+		}
+
+		// Default currency from the company
+		var currencyID int64
+		err := env.Tx().QueryRow(env.Ctx(),
+			`SELECT currency_id FROM res_company WHERE id = $1`, companyID).Scan(&currencyID)
+		if err == nil && currencyID > 0 {
+			vals["currency_id"] = currencyID
+		}
+
+		// Default date_order = now
+		vals["date_order"] = time.Now().Format("2006-01-02 15:04:05")
+
+		return vals
+	}
+
 	// -- Sequence Hook --
 	m.BeforeCreate = func(env *orm.Environment, vals orm.Values) error {
 		name, _ := vals["name"].(string)
 		if name == "" || name == "/" {
 			seq, err := orm.NextByCode(env, "sale.order")
-			if err == nil {
+			if err != nil {
+				// Fallback: generate a simple name like purchase.order does
+				vals["name"] = fmt.Sprintf("SO/%d", time.Now().UnixNano()%100000)
+			} else {
 				vals["name"] = seq
 			}
 		}