Add plain-language concept docs; fix docs viewer rendering; link API tokens

- New docs/concepts-{accounts,oauth-apps,api-tokens}.md -- plain-language
  guides aimed at less technical readers, each linking onward to the
  existing schema/protocol-level doc for anyone who wants that detail.
  Card help links (Users, Groups, OAuth cards, My groups, Members of
  <uid>'s group) now point here instead of straight at the technical
  docs; the LDAP-protocol-wiring cards (raw connection details for
  connecting a 3rd-party app) stay pointed at the technical ldap.md,
  since that's genuinely the right depth for that task.
- The "New API Token" card had no help link at all -- added, pointing to
  the new API Tokens doc.
- Fixed the in-app docs viewer rendering every docs/*.md page with a
  garbled heading + stray <hr> at the top: Jekyll front matter (meant
  only for the GitHub Pages build) was never stripped before being
  handed to the markdown renderer. Also fixed: cross-doc links
  (ldap.html, index.html, etc.) never resolved in-app, since this
  viewer serves docs at /docs/<slug> with no .html suffix -- rewritten
  to the correct in-app URL, same idea as the existing image-path fix.

Bumps to v1.1.12.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01KDEx8ghuZR61pqPXc6da9C

nodejs/package-lock.json

@@ -1,12 +1,12 @@
 {
   "name": "t42-sso-manager",
-  "version": "1.1.11",
+  "version": "1.1.12",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "t42-sso-manager",
-      "version": "1.1.11",
+      "version": "1.1.12",
       "license": "MIT",
       "dependencies": {
         "@fortawesome/fontawesome-free": "^7.3.0",