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/tech-debt-backlog/aidlc-state.md

@@ -0,0 +1,34 @@
+# AI-DLC State Tracking
+
+## Project Information
+- **Feature Name**: Tech Debt Backlog
+- **Feature Slug**: tech-debt-backlog
+- **Project Type**: Brownfield
+- **Start Date**: 2026-07-01T00:00:00Z
+- **Current Stage**: INCEPTION - Backlog captured, not yet triaged/prioritized
+- **Branch**: unknown
+
+## Workspace State
+- **Existing Code**: Yes
+- **Reverse Engineering Needed**: No (artifacts exist in `aidlc-docs/_shared/reverse-engineering/`)
+- **Workspace Root**: K:\Development\Projects\SlpModularCms
+
+## Code Location Rules
+- **Application Code**: Workspace root (NEVER in aidlc-docs/)
+- **Feature Documentation**: aidlc-docs/features/tech-debt-backlog/ only
+- **Shared Artifacts**: aidlc-docs/_shared/
+
+## Language Configuration
+- **Documentation Language**: English
+- **Conversation Language**: Dutch (User Language)
+
+## Purpose
+
+A running backlog of small, non-blocking issues discovered incidentally while working on other features (dead config, pre-existing lint findings, etc.). Items are captured here instead of fixed in-flight so they don't block the feature where they were found. Pick up and triage when convenient.
+
+## Stage Progress
+
+### 🔵 INCEPTION PHASE
+- [x] Workspace Detection — Complete (feature created ad-hoc during master-cms-module Build & Test)
+- [ ] Requirements Analysis — Backlog list captured in `inception/requirements/backlog.md`; not yet prioritized or scoped into units
+- [ ] Everything else — Not started; pick up when the user chooses to work this feature