Resolve doc cross-links by real filename as a fallback

The new concept docs (and their "See also" reciprocal links) reference
each other by real filename -- "concepts-accounts.html" -- which is the
correct, working URL on the Jekyll/GitHub Pages build (a page's URL there
IS its filename stem), but doesn't match this viewer's own short slugs
(DOCS keys, e.g. "accounts" -> /docs/accounts), so fixDocLinks() left
those links unrewritten and 404ing in-app.

Rather than rewrite the docs to two different link forms depending on
target, resolve by filename as a fallback when the slug lookup misses --
one link written in a doc now works correctly on both targets.

Bumps to v1.1.13.

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": "1.1.12",
+  "version": "1.1.13",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "t42-sso-manager",
-      "version": "1.1.12",
+      "version": "1.1.13",
       "license": "MIT",
       "dependencies": {
         "@fortawesome/fontawesome-free": "^7.3.0",