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/performance-test-instructions.md

@@ -0,0 +1,40 @@
+# Performance Test Instructions
+
+## Purpose
+Validate that the master-controlled availability gate does not introduce meaningful request latency on the slave, per NFR-PERF-01/PERF-02 (`aidlc-docs/features/master-cms-module/construction/slave-availability-extension/nfr-requirements/nfr-requirements.md`).
+
+## Performance Requirements
+No explicit throughput/latency SLA was defined during NFR Requirements for this feature. The design goal instead is architectural:
+- **PERF-01**: The slave's master-gate check reads a `volatile` static in-memory field — zero async overhead, zero DB call per request.
+- **PERF-02**: Only the local availability gate touches the DB, unchanged from pre-existing behavior (1s cache per `AvailabilityOptions.StatusCacheSeconds`).
+
+## Setup Performance Test Environment
+
+### 1. Prepare Test Environment
+```bash
+dotnet run --project src/SlpModularCms.Api --urls http://localhost:5002 --environment Production
+```
+
+### 2. Configure Test Parameters
+- **Test Duration**: 60 seconds
+- **Virtual Users**: 50 concurrent
+- **Target endpoint**: Any slave CMS route protected by `AvailabilityMiddleware`
+
+## Run Performance Tests
+
+### 1. Baseline (master-gate disabled / no `MasterRegistration` configured)
+```bash
+k6 run --vus 50 --duration 60s baseline-script.js
+```
+
+### 2. With Master-Gate Enabled (registered slave, `_masterIsAvailable = true`)
+```bash
+k6 run --vus 50 --duration 60s gated-script.js
+```
+
+### 3. Analyze Performance Results
+- **Expected**: p95 latency delta between baseline and gated runs should be negligible (sub-millisecond), since the gate check is a single `volatile` field read with no I/O.
+- **Bottlenecks**: If a measurable delta appears, verify no accidental DB or network call was introduced into `AvailabilityMiddleware`'s master-gate branch.
+
+## Performance Optimization
+Not applicable at this time — no bottleneck identified in code review or NFR design. Revisit only if production monitoring shows gate-related latency.