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

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+# 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

aidlc-docs/features/tech-debt-backlog/audit.md

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+# Audit Log — Tech Debt Backlog
+
+## Initial Request — Feature Created
+
+**Timestamp**: 2026-07-01T00:00:00Z
+
+**User Input**: "Laat ze staan en documenteer ze als unused. Maak ook een nieuwe feature aan waar je dit in verwerkt om te fixen dat ze niet worden gebruikt. Als je meer issues vindt gooi die dan ook in deze feature. Maak het dus eigenlijk een soort tech debt feature. Net als de gefaalde tests bij de Build & Test check die je zojuist gedaan hebt. Die tech debt feature kan ik dan later oppakken. Voor nu doorgaan met unit 4"
+
+**AI Response**: "Nieuwe feature 'tech-debt-backlog' aangemaakt als lichtgewicht backlog (geen volledige inception-cyclus doorlopen, gezien het doel puur registratie is voor latere oppak). Backlog vastgelegd in inception/requirements/backlog.md met 3 items: TD-001 (dode MasterModuleOptions properties), TD-002 (4 pre-existing frontend lint findings, geverifieerd via git worktree checkout van commit c156107 met schone npm install), TD-003 (2 nieuwe lint findings geïntroduceerd door master-cms-module Unit 3, bewust hierheen verplaatst i.p.v. direct gefixt). Toegevoegd aan active-features.md."
+
+**Context**: Feature aangemaakt tijdens master-cms-module sessie; geen actieve executie gestart, puur registratie voor later
+
+---

aidlc-docs/features/tech-debt-backlog/inception/requirements/backlog.md

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+# Tech Debt Backlog
+
+Items discovered incidentally while working on other features. Not yet prioritized. Each item lists where it was found and what "done" looks like.
+
+---
+
+## TD-001: Dead config properties on `MasterModuleOptions`
+
+**Found during**: `master-cms-module` — Build & Test / appsettings mapping (2026-07-01)
+
+**Location**: `src/SlpModularCms.Modules.Master/Options/MasterModuleOptions.cs`
+
+**Issue**: `CacheMinutes` and `ApiKey` are declared on the options POCO and were originally designed (per `aidlc-docs/features/master-cms-module/construction/master-backend/functional-design/domain-entities.md`) as slave-side settings for Unit 2 (slave-availability-extension) to consume. When Unit 2 was actually implemented, it used a different pattern instead — per-instance Data-Protection-encrypted API keys pushed from the Master, and a no-TTL in-memory cache (`REL-02` in the Availability NFR requirements) rather than a configurable `CacheMinutes`. As a result, neither property is read anywhere in the codebase.
+
+**Done looks like**: Either remove both properties from `MasterModuleOptions` (and any corresponding appsettings documentation), or — if a future feature revives the pull/TTL model — wire them up for real. Confirm via `grep -rn "CacheMinutes\|Options.Value.ApiKey" src/` that nothing reads them before removing.
+
+---
+
+## TD-002: Pre-existing frontend lint errors (react-hooks plugin)
+
+**Found during**: `master-cms-module` — Build & Test (2026-07-01), confirmed pre-existing via `git worktree` checkout of commit `c156107` (the commit immediately before this feature's frontend work) with a clean `npm install`
+
+**Issues** (4 total — 4 errors, 0 warnings at that baseline):
+1. `frontend/src/components/ui/badge.tsx:32` — `react-refresh/only-export-components`: the file exports both a component and a non-component value (likely `badgeVariants`), breaking Fast Refresh. Fix: move the shared constant/function to a separate file.
+2. `frontend/src/components/users/InviteUserDialog.tsx` — two related findings in the same `useEffect`:
+   - `react-hooks/set-state-in-effect`: `setStep(1)` (and sibling `setState` calls) run synchronously inside a `useEffect` that resets dialog state on close.
+   - `react-hooks/immutability`: `reset()` (from `useForm`) is referenced in the effect body before its `const { reset } = useForm(...)` declaration further down the component — works today due to hoisting/closure timing but is flagged as fragile.
+3. `frontend/src/pages/SettingsPage.tsx:39` — `react-hooks/set-state-in-effect`: `setSelectedMode`/`setReason` run synchronously inside a `useEffect` that syncs local form state from a query result (`availability`).
+
+**Done looks like**: Refactor each flagged effect per the React docs' "you might not need an effect" guidance (react.dev/learn/you-might-not-need-an-effect) — e.g. compute derived state during render, or move the reset logic into the `onOpenChange`/event handler instead of an effect. For `badge.tsx`, split the non-component export into its own module. Re-run `npm run lint` in `frontend/` until clean.
+
+---
+
+## TD-003: New lint findings introduced by `master-cms-module` Unit 3 (same pattern as TD-002)
+
+**Found during**: `master-cms-module` — Build & Test (2026-07-01). These were introduced by this feature's own Unit 3 (frontend-cms-page) code, but deferred here per explicit user decision (2026-07-01: "Laat ze staan... gooi die dan ook in deze feature") rather than fixed in-flight, to avoid blocking Unit 4.
+
+**Issues** (2 total — 1 error, 1 warning):
+1. `frontend/src/components/cms/AddCmsInstanceDialog.tsx:55` — `react-hooks/set-state-in-effect`: `setServerError(null)` (and sibling calls) run synchronously inside the dialog's close-reset `useEffect`. Same pattern as TD-002 item 2.
+2. `frontend/src/components/cms/SetStatusDialog.tsx:72` — `react-hooks/incompatible-library` (warning): `watch()` from `react-hook-form`'s `useForm()` is used directly; React Compiler can't safely memoize it, so compilation is skipped for this component/hook.
+
+**Done looks like**: Same remediation approach as TD-002 item 2 for the `AddCmsInstanceDialog.tsx` finding. For `SetStatusDialog.tsx`, either accept the compiler skipping memoization for this component (likely fine, low-traffic dialog) or replace `watch('status')` with a subscription-based pattern (`useWatch`) if it becomes a proven perf issue.
+
+---
+
+## Notes
+
+- None of these block functionality — `npm run build` and all test suites pass regardless.
+- TD-002 and TD-003 share the same underlying pattern (`setState` in a mount/close-reset effect) — worth fixing as one pass across all four files rather than one-by-one, once picked up.