[IMP] product_pricelist_total_margin: Add margin_type selector (Markup vs Commercial Margin)

- Add margin_type field to choose between calculation methods:
  * Markup (on cost): PVP = Cost × (1 + markup%)
  * Commercial Margin (on PVP): PVP = Cost / (1 - margin%)
- Update _compute_price() to apply correct formula based on margin_type
- Add safety cap for commercial margin >= 100% (caps at 99%)
- Add detailed logging for both calculation types
- Update views to show margin_type field when use_total_margin is enabled
- Add 2 new tests to validate both calculation methods:
  * test_total_margin_markup_type: validates markup formula
  * test_total_margin_commercial_margin_type: validates commercial margin formula
- All 11 tests passing (9 existing + 2 new)

Example with Commercial Margin:
Base: 4.68€, Total Margin: 20%
- Markup: 4.68 × 1.20 = 5.616€ (margin = 16.67% of PVP)
- Commercial Margin: 4.68 / 0.80 = 5.85€ (margin = 20% of PVP) ✓

product_pricelist_total_margin/tests/test_total_margin.py

@@ -351,3 +351,63 @@ class TestTotalMargin(TransactionCase):
         self.env["ir.config_parameter"].sudo().set_param(
             "product_pricelist_total_margin.max_percent", "0.0"
         )
+
+    def test_total_margin_markup_type(self):
+        """Test total margin with Markup calculation (on cost)."""
+        # Enable total margin and set to markup
+        self.item_base.use_total_margin = True
+        self.item_chained.use_total_margin = True
+        self.item_chained.margin_type = "markup"
+
+        price = self.pricelist_chained._get_product_price(
+            product=self.product,
+            quantity=1.0,
+        )
+
+        # Expected calculation (Markup):
+        # Base: 4.68
+        # Total margin: -5% + 25% = 20%
+        # Markup formula: PVP = Cost × (1 + markup%)
+        # Final: 4.68 * (1 + 0.20) = 5.616
+        expected_price = 4.68 * 1.20
+        self.assertAlmostEqual(
+            price,
+            expected_price,
+            places=2,
+            msg=f"Markup calculation should give {expected_price}, got {price}",
+        )
+
+    def test_total_margin_commercial_margin_type(self):
+        """Test total margin with Commercial Margin calculation (on PVP)."""
+        # Enable total margin and set to commercial margin
+        self.item_base.use_total_margin = True
+        self.item_chained.use_total_margin = True
+        self.item_chained.margin_type = "margin"
+
+        price = self.pricelist_chained._get_product_price(
+            product=self.product,
+            quantity=1.0,
+        )
+
+        # Expected calculation (Commercial Margin):
+        # Base: 4.68
+        # Total margin: -5% + 25% = 20%
+        # Commercial margin formula: PVP = Cost / (1 - margin%)
+        # Final: 4.68 / (1 - 0.20) = 5.85
+        expected_price = 4.68 / 0.80
+        self.assertAlmostEqual(
+            price,
+            expected_price,
+            places=2,
+            msg=f"Commercial margin calculation should give {expected_price}, got {price}",
+        )
+
+        # Verify the commercial margin is indeed 20%
+        # Commercial margin = (PVP - Cost) / PVP
+        commercial_margin = (price - 4.68) / price
+        self.assertAlmostEqual(
+            commercial_margin,
+            0.20,
+            places=4,
+            msg=f"Commercial margin should be 20%, got {commercial_margin * 100}%",
+        )