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/construction/build-and-test/build-instructions.md

@@ -0,0 +1,32 @@
+# Build Instructions
+
+## Prerequisites
+- **Build Tool**: .NET SDK 10 (backend), Node.js + npm/pnpm (frontend)
+- **Dependencies**: NuGet packages (restored automatically), npm packages in `frontend/`
+- **Environment Variables**: None required for build
+- **System Requirements**: Windows/Linux/macOS, .NET 10 runtime
+
+## Build Steps
+
+### 1. Backend — Install Dependencies & Build
+```bash
+dotnet build SlpModularCms.sln
+```
+
+### 2. Frontend — Install Dependencies & Build
+```bash
+cd frontend
+npm install
+npm run build   # tsc -b && vite build
+```
+
+## Verify Build Success
+- **Backend**: `Build succeeded. 0 Error(s)` — all 9 projects compile (Core, Modules.Identity, Modules.Availability, Modules.Master, Api, plus 4 test projects)
+- **Frontend**: Vite produces a `dist/` bundle with no TypeScript errors
+- **Build Artifacts**: `src/**/bin/Debug/net10.0/*.dll`, `frontend/dist/`
+
+## Troubleshooting
+
+### TypeScript build fails with mutation callback arity errors
+- **Cause**: `@tanstack/react-query` v5.101 changed the `onSuccess` mutation callback signature to include a 4th `context` parameter. Manually calling `options?.onSuccess?.(data, variables, context)` with only 3 args now under-supplies the callback's expected arity.
+- **Solution**: Forward all trailing callback args with a rest parameter, e.g. `onSuccess: (data, variables, ...rest) => { ...; options?.onSuccess?.(data, variables, ...rest); }`. Fixed in `frontend/src/api/useUpdateCmsInstanceStatus.ts`.