feat: add alternate UOM balance columns to Stock Balance report

Closes #52953

The Stock Balance report previously showed balance qty only in the item's
stock UOM. To view balance in an alternate UOM, users had to set the
"Include UOM" filter — which applies a single UOM to all items. This breaks
down when different items use different alternate UOMs (e.g., Pens in Box,
Ink in Milliliters).

This change adds a new "Show Alternate UOM Balance" checkbox filter. When
enabled, up to two alternate UOM columns are injected right after the
Balance Qty column:

  Balance Qty | Alt UOM 1 | Balance Qty (Alt UOM 1) | Alt UOM 2 | Balance Qty (Alt UOM 2)

Each row resolves its own alternate UOMs from `tabUOM Conversion Detail`
(ordered by idx, excluding the item's stock UOM). The converted balance
qty is computed as: stock qty / conversion_factor.

Items with fewer than 2 alternate UOMs leave the extra columns blank.
The existing "Include UOM" filter behaviour is unchanged.

(cherry picked from commit 2d93c5835a)

erpnext/stock/report/stock_balance/stock_balance.js

@@ -110,6 +110,12 @@ frappe.query_reports["Stock Balance"] = {
 			fieldtype: "Link",
 			options: "UOM",
 		},
+		{
+			fieldname: "show_alt_uom_balance",
+			label: __("Show Alternate UOM Balance"),
+			fieldtype: "Check",
+			default: 0,
+		},
 		{
 			fieldname: "show_variant_attributes",
 			label: __("Show Variant Attributes"),

erpnext/stock/report/stock_balance/stock_balance.py

@@ -35,6 +35,7 @@ class StockBalanceFilter(TypedDict):
 	include_uom: str | None  # include extra info in converted UOM
 	show_stock_ageing_data: bool
 	show_variant_attributes: bool
+	show_alt_uom_balance: bool
 
 
 SLEntry = dict[str, Any]
@@ -76,6 +77,7 @@ class StockBalanceReport:
 			self.columns = self.get_columns()
 
 		self.add_additional_uom_columns()
+		self.add_alt_uom_columns()
 
 		return self.columns, self.data
 
@@ -602,6 +604,86 @@ class StockBalanceReport:
 		conversion_factors = self.get_itemwise_conversion_factor()
 		add_additional_uom_columns(self.columns, self.data, self.filters.include_uom, conversion_factors)
 
+	def add_alt_uom_columns(self) -> None:
+		"""Add up to 2 alternate UOM balance columns per item after the Balance Qty column."""
+		if not self.filters.get("show_alt_uom_balance"):
+			return
+
+		item_alt_uom_map = self.get_item_alt_uom_map()
+		if not item_alt_uom_map:
+			return
+
+		# Insert columns right after bal_qty (in reverse order so slot 1 comes first)
+		bal_qty_idx = next(
+			(i for i, col in enumerate(self.columns) if isinstance(col, dict) and col.get("fieldname") == "bal_qty"),
+			None,
+		)
+		if bal_qty_idx is None:
+			return
+
+		for slot in (2, 1):
+			self.columns.insert(
+				bal_qty_idx + 1,
+				{
+					"label": _(f"Balance Qty (Alt UOM {slot})"),
+					"fieldname": f"alt_uom_{slot}_bal_qty",
+					"fieldtype": "Float",
+					"width": 140,
+				},
+			)
+			self.columns.insert(
+				bal_qty_idx + 1,
+				{
+					"label": _(f"Alt UOM {slot}"),
+					"fieldname": f"alt_uom_{slot}",
+					"fieldtype": "Data",
+					"width": 90,
+				},
+			)
+
+		for row in self.data:
+			alt_uoms = item_alt_uom_map.get(row.item_code, [])
+			for slot in (1, 2):
+				idx = slot - 1
+				if idx < len(alt_uoms):
+					uom, factor = alt_uoms[idx]["uom"], flt(alt_uoms[idx]["conversion_factor"])
+					row[f"alt_uom_{slot}"] = uom
+					row[f"alt_uom_{slot}_bal_qty"] = flt(row.get("bal_qty", 0)) / factor if factor else 0.0
+				else:
+					row[f"alt_uom_{slot}"] = ""
+					row[f"alt_uom_{slot}_bal_qty"] = 0.0
+
+	def get_item_alt_uom_map(self) -> dict:
+		"""Return {item_code: [{uom, conversion_factor}, ...]} for alternate UOMs (excluding stock UOM)."""
+		item_codes = list({d["item_code"] for d in self.data})
+		if not item_codes:
+			return {}
+
+		uom_detail = frappe.qb.DocType("UOM Conversion Detail")
+		item_table = frappe.qb.DocType("Item")
+
+		rows = (
+			frappe.qb.from_(uom_detail)
+			.join(item_table)
+			.on(uom_detail.parent == item_table.name)
+			.select(uom_detail.parent, uom_detail.uom, uom_detail.conversion_factor)
+			.where(
+				(uom_detail.parenttype == "Item")
+				& (uom_detail.parent.isin(item_codes))
+				& (uom_detail.uom != item_table.stock_uom)
+			)
+			.orderby(uom_detail.parent)
+			.orderby(uom_detail.idx)
+		).run(as_dict=True)
+
+		result: dict = {}
+		for row in rows:
+			result.setdefault(row.parent, [])
+			if len(result[row.parent]) < 2:  # keep up to 2 alternate UOMs
+				result[row.parent].append({"uom": row.uom, "conversion_factor": row.conversion_factor})
+
+		return result
+
 	def get_itemwise_conversion_factor(self):
 		items = []
 		if self.filters.item_code or self.filters.item_group: