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

extension/dashboard/pages/settings.js

@@ -35,11 +35,13 @@ function updateSettingsUI() {
   const backupRetentionEl = $('backupRetention');
   const backupIntervalEl = $('backupIntervalHours');
   const latencyPingIntervalEl = $('latencyPingIntervalMs');
+  const dashboardRefreshEl = $('dashboardRefreshIntervalMs');
   if (proxyPortEl) proxyPortEl.value = settings.proxyPort ?? SETTINGS_DEFAULTS.proxyPort;
   if (readyTimeoutMsEl) readyTimeoutMsEl.value = settings.readyTimeoutMs ?? SETTINGS_DEFAULTS.readyTimeoutMs;
   if (backupRetentionEl) backupRetentionEl.value = settings.backupRetention ?? SETTINGS_DEFAULTS.backupRetention;
   if (backupIntervalEl) backupIntervalEl.value = settings.backupIntervalHours ?? SETTINGS_DEFAULTS.backupIntervalHours;
   if (latencyPingIntervalEl) latencyPingIntervalEl.value = (settings.latencyPingIntervalMs ?? SETTINGS_DEFAULTS.latencyPingIntervalMs) / 1000;
+  if (dashboardRefreshEl) dashboardRefreshEl.value = String(settings.dashboardRefreshIntervalMs ?? SETTINGS_DEFAULTS.dashboardRefreshIntervalMs ?? 2000);
 }
 
 function saveSettings() {
@@ -57,6 +59,8 @@ function saveSettings() {
   settings.latencyPingIntervalMs = isNaN(pingSecs) || pingSecs <= 0
     ? SETTINGS_DEFAULTS.latencyPingIntervalMs
     : Math.round(pingSecs * 1000);
+  const refreshVal = parseInt($('dashboardRefreshIntervalMs')?.value, 10);
+  settings.dashboardRefreshIntervalMs = ([0, 2000, 5000, 10000].includes(refreshVal) ? refreshVal : SETTINGS_DEFAULTS.dashboardRefreshIntervalMs);
   chrome.runtime.sendMessage(
     { target: 'holesail-native', action: 'send', payload: { type: 'updateSettings', payload: { ...settings } } },
     (response) => {
@@ -66,6 +70,7 @@ function saveSettings() {
         _clearSettingsDirty();
         // Restart the ping interval so the new interval / enabled state takes effect immediately
         if (typeof window._restartPingInterval === 'function') window._restartPingInterval();
+        if (typeof window._restartRefreshInterval === 'function') window._restartRefreshInterval();
         if (response.requiresRestart) {
           showToast('Settings saved — restart the native host for proxy port changes to take effect', 'warning');
         } else {