Completes local-dev-master-slave-setup: dual-instance frontend tooling, module-capability gating, and master/slave protocol self-healing fixes

Frontend (Unit 2 completion): dual dev-server tooling (pnpm dev:slave,
pnpm dev:all), per-instance browser tab titles, and a backend
capability check (SystemController + useSystemCapabilities +
ModuleGuard) so a Master-only page is hidden on a slave instance
instead of assuming every backend has every module.

Master/slave protocol fixes surfaced by actually running master and
slave side by side locally:
- Deactivating a CMS instance (Inactive) now releases the slave's
  master gate instead of leaving it stuck on its last pushed status.
- The periodic integrity check now also re-pushes status to every
  reachable slave (previously URL-verification only) and runs once
  immediately on startup.
- Added the originally-specified (but never implemented) slave-pull
  path: a slave now periodically polls its own status from the master
  (GET /api/v1/SlaveStatus) and fails open to Available if the master
  is unreachable for too long, complementing the existing push.
- The slave's own Settings page can no longer "successfully" change
  local availability while the master controls it; it's now locked
  with an explanatory banner and the backend rejects the write with
  409 instead of silently no-op'ing it.
- CMS instance status badges now match the dashboard's color/icon
  styling instead of a plain grey badge.

Also corrected the master-cms-module design docs to match this
as-built behavior, and flagged (without a full rewrite) a larger,
pre-existing divergence between its inception-stage application
design and what construction actually built.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

aidlc-docs/features/master-cms-module/inception/application-design/services.md

@@ -1,5 +1,7 @@
 # Services — Master CMS Module
 
+> ⚠️ **Superseded, found stale 2026-07-04**: this document is the *inception-stage* design and describes an earlier pull-based `IMasterAvailabilityService` (static cache + `MasterModuleOptions.CacheMinutes` + `/api/internal/master/*` routes) that was **not what got built**. Construction pivoted to a push-based protocol instead (`/api/v1/master/*` routes, `_masterIsAvailable`/`_masterDisableMessage` fields, no `CacheMinutes`). A slave-pull mechanism was eventually added too, but on 2026-07-04 and with a different shape (`MasterStatusPollingBackgroundService` polling `GET /api/v1/SlaveStatus` on an interval, with a time-based fail-open) than what's described below. **Treat this file as historical intent, not current truth** — the accurate, as-built design lives in `construction/master-backend/functional-design/*.md` and `construction/slave-availability-extension/functional-design/*.md`. This divergence predates 2026-07-04 and was found (not caused) during today's documentation audit; `CacheMinutes`/`ApiKey` dead-config fallout is already tracked as TD-001 in `tech-debt-backlog`.
+
 ## Service Definitions
 
 ### Master-Side Services