fix(system): report real version so update banner clears; move update notice to Operations (v0.16.11-beta)

Update-availability fixes:
- The backend read its version from npm_package_version, which is unset
  when the container runs `node dist/index.js` directly, so current was
  always "0.0.0" and every release looked newer — the "update available"
  banner never cleared. Read the bundled package.json instead
  (routes/system.ts), falling back to npm_package_version.
- Move the update notification out of the top-of-app banner into the
  Operations dashboard (a dedicated notice under the network-status hero),
  shown only when genuinely behind and cleared once up to date.

Security banner:
- Replace the now-dead jwt_secret_default / encryption_key_default checks
  with the current secrets_not_persisted warning (auto-generated secrets
  that couldn't be persisted), matching the self-healing secrets model.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

backend/package.json

@@ -1,6 +1,6 @@
 {
   "name": "mikrotik-manager-backend",
-  "version": "0.16.10-beta",
+  "version": "0.16.11-beta",
   "description": "Mikrotik Network Management Platform - Backend API",
   "main": "dist/index.js",
   "scripts": {