fix: site name in top logo + server-list public + external API docs page

- app.js: set #logo-text (top bar) from window.__SITE_NAME__ - the
  top-right site name stayed default because only #site-title and
  #sidebar-title were set
- security.js: apiKeyGuard whitelist /api/polls/server-list so the
  ticket create page can load sub-servers (was 401 without api key)
- external-api.js: management page now only creates/manages clients,
  removed inline endpoint table
- new external-api-docs.js: full API doc page (auth flow, all 11
  endpoints, request/response examples, Node sample) at
  #/external-api-docs, linked from the management page
- index.html: load external-api-docs.js

public/index.html

@@ -70,6 +70,7 @@
   <script src="js/pages/templates.js"></script>
   <script src="js/pages/notifications.js"></script>
   <script src="js/pages/external-api.js"></script>
+  <script src="js/pages/external-api-docs.js"></script>
   <script src="js/pages/settings-page.js"></script>
   <script src="js/pages/export-page.js"></script>
   <script src="js/pages/polls.js"></script>