Add bundle sales backend implementation

docs/14-BACKEND-SALES-API.md

@@ -1,6 +1,6 @@
 # 14 · BACKEND — Sales API Reference
 
-> **Authoritative for:** sales API contracts for invoices, slips, free issues, and sales reports.
+> **Authoritative for:** sales API contracts for invoices, slips, bundle sales, free issues, and sales reports.
 > **Navigation:** start from `00-CORE.md`. Sales business rules live in `docs/SALES_MODULE_PLAN.md` and the sales-related backend progress is tracked in `Backend/PROGRESS.md`.
 > **Scope:** this document covers the sales endpoints currently implemented in ERPCore. Free issue is modeled as a sales-slip alias, not a separate table.
 
@@ -132,9 +132,62 @@ Before posting, the UI calls `GET /api/v1/sales-slips/{salesSlipId}/posting-chec
 ### `POST /api/v1/sales-slips/{salesSlipId}/cancel`
 Cancels a draft slip.
 
+--- 
+
+## 4. Bundle Sales
+
+Bundle sales are a separate sales document family for fixed bundle compositions.
+
+### `GET /api/v1/bundle-sales`
+Query:
+- `page`
+- `pageSize`
+- `q`
+- `customerId`
+- `warehouseId`
+
+Returns a paged list of `BundleSaleSummaryDto`.
+
+### `GET /api/v1/bundle-sales/{bundleSaleId}`
+Returns `BundleSaleDto`.
+
+### `GET /api/v1/bundle-sales/{bundleSaleId}/posting-check`
+Validates component stock before posting.
+
+### `POST /api/v1/bundle-sales`
+Creates a draft bundle sale from a fixed template.
+
+Request:
+```json
+{
+  "customerId": 2,
+  "warehouseId": 1,
+  "cashierUserId": 1,
+  "bundleSaleTemplateId": 1,
+  "bundleName": "Summer Promo Pack",
+  "bundleCode": "BND-001",
+  "bundlePrice": 2500,
+  "allowPriceOverride": true
+}
+```
+
+### `PUT /api/v1/bundle-sales/{bundleSaleId}`
+Updates a draft bundle sale. Requires `If-Match`.
+
+### `POST /api/v1/bundle-sales/{bundleSaleId}/post`
+Posts the bundle and consumes stock from the included component lines.
+
+### `POST /api/v1/bundle-sales/{bundleSaleId}/cancel`
+Cancels a draft bundle sale.
+
+Business rule:
+- bundle composition is fixed by template lines
+- posting consumes component stock, not a synthetic bundle stock item
+- print pages should show both the bundle summary and the component breakdown
+
 ---
 
-## 4. Free Issues
+## 5. Free Issues
 
 Free issue is a business alias over sales slips.
 There is no separate free-issue table in the current schema.
@@ -165,7 +218,7 @@ Business rule:
 
 ---
 
-## 5. Sales Reports
+## 6. Sales Reports
 
 ### `GET /api/v1/reports/sales`
 Returns the report catalog.
@@ -217,8 +270,9 @@ Validation rule:
 
 ---
 
-## 6. Notes
+## 7. Notes
 
 - The sales report service reads both invoices and slips where relevant.
 - Free issue reporting is derived from the same sales document lines.
+- Bundle sales are treated as a separate fixed-composition document family.
 - There is no separate free-issue table in the current schema.