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/overview.js

@@ -1,9 +1,17 @@
-// Depends on: core/utils.js ($, escapeHtml), ui/state-tag.js (stateTag),
-//             ui/modal.js (openModal), pages/ssh.js (openAddSshModal),
-//             pages/rdp.js (openAddRdpModal), core/state.js (sshConnections, rdpConnections)
+/**
+ * Overview page — summary stats, quick-action cards, and virtualized connection lists.
+ * Uses the OvList class for infinite-scroll, searchable tables of connections and servers.
+ * Depends on: core/utils.js ($, escapeHtml), ui/state-tag.js (stateTag),
+ *             ui/modal.js (openModal), pages/ssh.js (openAddSshModal),
+ *             pages/rdp.js (openAddRdpModal), core/state.js (sshConnections, rdpConnections)
+ */
 
 const OV_PAGE = 20; // rows per page
 
+/**
+ * Virtualized, searchable, infinite-scroll list for the Overview page.
+ * Renders rows in pages of OV_PAGE, loading more when the sentinel element scrolls into view.
+ */
 class OvList {
   constructor({ bodyId, sentinelId, searchId, subtitleId, rowFn, emptyMsg, cols }) {
     this.body       = $(bodyId);
@@ -78,6 +86,10 @@ let _ovSvc     = null;
 let _ovSsh     = null;
 let _ovRdp     = null;
 
+/**
+ * Create and wire up the OvList instances for virtual hosts and server tunnels.
+ * Called once during dashboard initialisation.
+ */
 function initOvLists() {
   _ovVhost = new OvList({
     bodyId: 'recentConnections', sentinelId: 'ovVhostSentinel',
@@ -175,6 +187,11 @@ function initOvLists() {
   $('qaInstallCA') ?.addEventListener('click', () => openModal('modal-installCA'));
 }
 
+/**
+ * Render the Overview page with the latest extension state.
+ * Updates summary stat cards, quick-action buttons, and the connection/server lists.
+ * @param {object} state - Full extension state from `fetchState()`.
+ */
 function updateDashboard(state) {
   currentState = state;
   const servers        = state.servers        || [];