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/logs.js

@@ -1,7 +1,15 @@
-// Depends on: core/utils.js ($, escapeHtml), ui/toast.js (showToast)
+/**
+ * Logs page — registers the dashboard with the background to receive live log events,
+ * renders a filterable/searchable log list with level filtering and auto-scroll toggle.
+ * Depends on: core/utils.js ($, escapeHtml), ui/toast.js (showToast)
+ */
 
 let _logsSetup = false;
 
+/**
+ * Set up the Logs page: register for live log broadcasts, wire up filter/search/scroll controls.
+ * Guarded by `_logsSetup` to prevent duplicate registration.
+ */
 function setupLogsEvents() {
   if (_logsSetup) return;
   _logsSetup = true;