eat: implement Holesail-Browser enhancement plan

- Add unit tests (hostname-validator, TLDs, payload-schemas) and integration tests for message handler registry
- Refactor native host message router into handler registry (handlers/state, tunnels, ssh, rdp, backup, ca, connections)
- Add ESLint config and npm test + lint steps in CI
- Dashboard: visibility-based refresh pause, configurable refresh interval (2s/5s/10s/paused)
- Accessibility: ARIA on nav and modals, focus trap and restore, prefers-reduced-motion
- Empty states: primary action buttons for virtual hosts, servers, service tunnels
- Native host rate limiting for backup and CA operations; update SECURITY.md
- CONTRIBUTING: "Adding a new dashboard page", dev workflow; add npm run dev script

native-host/holesail-manager/settings.js

@@ -44,6 +44,9 @@ function updateSettings(patch) {
   if (typeof patch.tunnelAutoReconnect === 'boolean') currentSettings.tunnelAutoReconnect = patch.tunnelAutoReconnect;
   if (typeof patch.latencyPingEnabled === 'boolean') currentSettings.latencyPingEnabled = patch.latencyPingEnabled;
   if (typeof patch.latencyPingIntervalMs === 'number' && patch.latencyPingIntervalMs > 0) currentSettings.latencyPingIntervalMs = patch.latencyPingIntervalMs;
+  if (typeof patch.dashboardRefreshIntervalMs === 'number' && patch.dashboardRefreshIntervalMs >= 0 && [0, 2000, 5000, 10000].includes(patch.dashboardRefreshIntervalMs)) {
+    currentSettings.dashboardRefreshIntervalMs = patch.dashboardRefreshIntervalMs;
+  }
   if (_saveState) _saveState();
   return { requiresRestart };
 }