Fix competitor price display and pricelist item deduplication

- Render competitor prices in Pricing tab (all three row branches)
- Add footer total accumulation for competitor column
- Deduplicate local_pricelist_items via migration + unique index
- Use ON CONFLICT DO NOTHING in SaveLocalPricelistItems to prevent duplicates on concurrent sync

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

internal/localdb/migrations.go

@@ -119,6 +119,11 @@ var localMigrations = []localMigration{
 		name: "Convert local partnumber book cache to book membership + deduplicated PN catalog",
 		run:  migrateLocalPartnumberBookCatalog,
 	},
+	{
+		id:   "2026_03_13_pricelist_items_dedup_unique",
+		name: "Deduplicate local_pricelist_items and add unique index on (pricelist_id, lot_name)",
+		run:  deduplicatePricelistItemsAndAddUniqueIndex,
+	},
 }
 
 type localPartnumberCatalogRow struct {
@@ -1092,3 +1097,26 @@ func rebuildLocalPartnumberBookCatalog(tx *gorm.DB, catalog map[string]*localPar
 	}
 	return nil
 }
+
+func deduplicatePricelistItemsAndAddUniqueIndex(tx *gorm.DB) error {
+	// Remove duplicate (pricelist_id, lot_name) rows keeping only the row with the lowest id.
+	if err := tx.Exec(`
+		DELETE FROM local_pricelist_items
+		WHERE id NOT IN (
+			SELECT MIN(id) FROM local_pricelist_items
+			GROUP BY pricelist_id, lot_name
+		)
+	`).Error; err != nil {
+		return fmt.Errorf("deduplicate local_pricelist_items: %w", err)
+	}
+
+	// Add unique index to prevent future duplicates.
+	if err := tx.Exec(`
+		CREATE UNIQUE INDEX IF NOT EXISTS idx_local_pricelist_items_pricelist_lot_unique
+		ON local_pricelist_items(pricelist_id, lot_name)
+	`).Error; err != nil {
+		return fmt.Errorf("create unique index on local_pricelist_items: %w", err)
+	}
+	slog.Info("deduplicated local_pricelist_items and added unique index")
+	return nil
+}