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/pages/service-tunnels.js

@@ -1,5 +1,9 @@
-// Depends on: core/utils.js ($, escapeHtml, truncate), ui/state-tag.js (stateTag),
-//             ui/toast.js (showToast, copyToClipboard), ui/modal.js (openModal, closeModal, showModalError)
+/**
+ * Service Tunnels page — renders the service tunnels table, manages bulk selection,
+ * and wires up add/edit/remove modal events.
+ * Depends on: core/utils.js ($, escapeHtml, truncate), ui/state-tag.js (stateTag),
+ *             ui/toast.js (showToast, copyToClipboard), ui/modal.js (openModal, closeModal, showModalError)
+ */
 
 function _updateSvcBulkBar() {
   const checked = document.querySelectorAll('#serviceTunnelsTable input[type="checkbox"]:checked');
@@ -14,6 +18,10 @@ function _updateSvcBulkBar() {
   }
 }
 
+/**
+ * Re-render the service tunnels table with the latest state.
+ * @param {object} state - Full extension state from `fetchState()`.
+ */
 function updateServiceTunnelsTable(state) {
   const tbody = $('serviceTunnelsTable');
   if (!tbody) return;
@@ -149,6 +157,10 @@ function updateServiceTunnelsTable(state) {
   _updateSvcBulkBar();
 }
 
+/**
+ * Attach all event listeners for the Service Tunnels page.
+ * Called once during dashboard initialisation.
+ */
 function setupServiceTunnelEvents() {
   $('svcSelectAll')?.addEventListener('change', (e) => {
     document.querySelectorAll('#serviceTunnelsTable .svc-row-cb').forEach(cb => { cb.checked = e.target.checked; });