Completes master-cms-module: Build & Test, docs, and appsettings

Finishes the master-cms-module feature (Units 1-4): runs Build and
Test across master-backend, slave-availability-extension and
frontend-cms-page, fixes a missing Availability EF migration for
MasterRegistration and a TanStack Query v5 mutation-callback type
break, adds the missing MasterModule appsettings section, and
documents the module in README.md. Also seeds a tech-debt-backlog
feature to track dead config and pre-existing/introduced frontend
lint findings for later cleanup.

aidlc-docs/features/master-cms-module/aidlc-state.md

@@ -5,7 +5,7 @@
 - **Feature Slug**: master-cms-module
 - **Project Type**: Brownfield
 - **Start Date**: 2026-06-26T00:00:00Z
-- **Current Stage**: CONSTRUCTION - Unit 3 (frontend-cms-page) Code Generation Complete
+- **Current Stage**: COMPLETE - All 4 units done, Build and Test passed, Unit 4 approved
 - **Branch**: unknown
 
 ## Workspace State
@@ -55,9 +55,11 @@
 - [x] NFR Requirements — Complete (Unit 3)
 - [x] NFR Design — Complete (Unit 3)
 - [x] Code Generation — Complete (Unit 3)
-- [ ] Infrastructure Design — Skipped
-- [ ] Code Generation — Execute (per unit)
-- [ ] Build and Test — Execute
+- [x] Infrastructure Design — Skipped (Units 1-3)
+- [x] Code Generation — Complete (Units 1-3)
+- [x] Build and Test — Complete (Units 1-3: build success, 402 automated tests pass)
+- [x] Functional Design — Skipped (Unit 4 - documentation only, no business logic)
+- [x] Code Generation — Complete (Unit 4 - documentation: README.md, frontend/README.md, appsettings.json/Development.json)
 
 ### 🟡 OPERATIONS PHASE
-- [ ] Operations — Placeholder
+- [x] Operations — Placeholder acknowledged; workflow complete