docs: add CONTRIBUTING.md, CHANGELOG.md, and JSDoc to entire codebase

Add docs/CONTRIBUTING.md covering the build system, dev workflow, all
npm scripts, how to add new native host message types, code style, and
debugging guidance.

Add CHANGELOG.md at the project root documenting all features and fixes
across the 1.0.0 release.

Add JSDoc (@param, @returns) to all previously undocumented exported
functions across 35 JS files:
- native-host/holesail-manager/ (index, virtual-hosts, service-tunnels,
  servers, port-allocator)
- native-host top-level managers (startup, connect-proxy, https-proxy,
  certificate-authority, ssh-manager, rdp-manager)
- extension/background/ (logs, native-messaging, proxy, message-router)
- extension/dashboard/core/ (utils, navigation, init)
- extension/dashboard/ui/ (modal, toast, state-tag)
- extension/dashboard/pages/ (all 10 page files)
- extension/dashboard/refresh.js, events.js
- extension/dashboard/data/hostname-validator.js
- scripts/ (build-host, run-install)

extension/dashboard/events.js

@@ -1,6 +1,14 @@
-// Global event wiring — toggle switches, settings buttons, and per-page setup calls.
-// Depends on: all page modules
+/**
+ * Global event wiring for the dashboard.
+ * Wires toggle switches (theme, notifications, auto-reconnect), settings buttons,
+ * export/import handlers, Holesail Lookup, and calls each page module's setup function.
+ * Depends on: all page modules
+ */
 
+/**
+ * Attach all global dashboard event listeners.
+ * Guarded by `document._holesailEventsSetup` to prevent duplicate registration.
+ */
 function setupEvents() {
   // Guard against duplicate listener registration if setupEvents() is called
   // more than once (e.g. after a hot-reload). Without this, anonymous listeners