implement fe with backend

docs/00-CORE.md

@@ -21,6 +21,7 @@ A modular ERP built in phases. **Phase 1** delivers the **Inventory & Supply Cha
 Full requirements live in the backend spec (see §7). This file does **not** duplicate them.
 
 **Phase 2 (HRM)** is now underway alongside Phase 1 — see §7 routing to `12-BACKEND-HRM.md` / `13-BACKEND-HRM-API.md` / `21-FRONTEND-HRM.md`.
+Sales has its own API reference at `14-BACKEND-SALES-API.md`.
 
 ---
 
@@ -45,6 +46,7 @@ erp-monorepo/
     ├── 02-SECURITY.md            # accepted-risks register + per-feature security checklist
     ├── 10-BACKEND-PHASE1.md      # backend spec: SRS + ER/entities + tech + architecture
     ├── 11-BACKEND-PHASE1.md      # backend API reference (complete req/res)
+    ├── 14-BACKEND-SALES-API.md   # sales API reference (invoices, slips, free issues, reports)
     ├── 12-GENERAL-LEDGER-INTEGRATION.md  # ERPCore ↔ external General Ledger service (transport only)
     ├── 20-FRONTEND.md            # frontend user-flows + architecture rules + validation posture
     └── 21-GENERAL-LEDGER-FRONTEND.md  # Ledgers section: reports UI + cash/bank accounts
@@ -344,6 +346,7 @@ All frontend work is governed by `20-FRONTEND.md`.
 | HRM API endpoints, request/response shapes, error catalog (Phase 2) | **`13-BACKEND-HRM-API.md`** |
 | Connecting to the external General Ledger service (proxy, config, API key) | **`12-GENERAL-LEDGER-INTEGRATION.md`** |
 | The Ledgers frontend section (reports, cash/bank accounts) | **`21-GENERAL-LEDGER-FRONTEND.md`** |
+| Sales API endpoints, request/response shapes, error catalog, enums | **`14-BACKEND-SALES-API.md`** |
 | Frontend user-flows, screen flow, architecture rules, validation posture (Phase 1) | **`20-FRONTEND.md`** |
 | HRM frontend user-flows (Phase 2) | **`21-FRONTEND-HRM.md`** |
 | Manufacturing requirements, business rules, entities, stock/costing integration, API (Phase 2) | **`30-BACKEND-PHASE2.md`** |
@@ -356,6 +359,7 @@ All frontend work is governed by `20-FRONTEND.md`.
 Quick resolver:
 - *"Where is the model / an entity defined?"* → `10-BACKEND-PHASE1.md` (Phase 1) / `12-BACKEND-HRM.md` (HRM) — schema is authoritative there.
 - *"What does this endpoint accept/return?"* → `11-BACKEND-PHASE1.md` (Phase 1) / `13-BACKEND-HRM-API.md` (HRM).
+- *"What does the sales API accept/return?"* → `14-BACKEND-SALES-API.md`.
 - *"How should the UI flow / what do I validate where?"* → `20-FRONTEND.md` (Phase 1) / `21-FRONTEND-HRM.md` (HRM).
 - *"What security risks / checks apply to this feature?"* → `02-SECURITY.md`.