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/host/handlers/rdp.js

@@ -0,0 +1,33 @@
+/**
+ * Handlers for RDP/VNC sessions.
+ * Context: rdpManager, debugLog
+ */
+
+function register(deps) {
+  const { rdpManager, debugLog } = deps;
+  return [
+    {
+      type: 'startRdpSession',
+      handle: async (payload, reply) => {
+        debugLog('startRdpSession: type=', payload.type, 'label=', payload.label);
+        const result = await rdpManager.startSession(payload);
+        debugLog('startRdpSession: result=', JSON.stringify({ ok: result.ok, sessionId: result.sessionId, wsPort: result.wsPort }));
+        reply(result);
+      }
+    },
+    {
+      type: 'stopRdpSession',
+      handle: async (payload, reply) => {
+        debugLog('stopRdpSession: sessionId=', payload.sessionId);
+        const result = await rdpManager.stopSession(payload);
+        reply(result);
+      }
+    },
+    {
+      type: 'getRdpSessions',
+      handle: async (payload, reply) => reply({ ok: true, sessions: rdpManager.getSessions() })
+    }
+  ];
+}
+
+module.exports = { register };