fix(hub): CI link audit accepts bare ../learnstack directory link

The follow-up CI fix in 917f7ec used `^(\.\./)+learnstack/` which requires
a trailing slash after `learnstack` — bare directory links like
`[LearnStack core](../learnstack)` (CONTRIBUTING.md:3) failed the audit:

    BROKEN: CONTRIBUTING.md → ../learnstack
    Error: 1 broken relative link(s) in changed Markdown.

Relaxed the regex to `^(\.\./)+learnstack(/|$)` so it matches both
`../learnstack` (bare root link) and `../learnstack/...` (path into the
sibling repo). The boundary is still tight — `../learnstackish/foo` does
not match (the regex anchors `learnstack` at a `/` or end-of-string).

Smoke-tested locally:
  ../learnstack             → MATCH
  ../learnstack/foo.md      → MATCH
  ../../../learnstack       → MATCH
  ../../learnstack/         → MATCH
  ../other                  → NOMATCH
  ../learnstackish/foo      → NOMATCH

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

Author: cemililik

.github/workflows/ci.yml

@@ -205,10 +205,14 @@ jobs:
                   #   - docs/*.md:                            ../../learnstack/...
                   #   - docs/{architecture,decisions}/*.md:   ../../../learnstack/...
                   #   - backend/src/Modules/README.md:        ../../../../learnstack/...
-                  # CI cannot reach the sibling repo, so skip the file-existence
-                  # check for any `(../)+learnstack/...` link. The links are
-                  # validated locally on the developer's workstation.
-                  if [[ "$link" =~ ^(\.\./)+learnstack/ ]]; then
+                  # The trailing piece is optional — `../learnstack` (a bare
+                  # directory link to the sibling repo's root) is just as
+                  # legitimate as `../learnstack/docs/...`. CI cannot reach
+                  # the sibling repo, so skip the file-existence check for
+                  # any `(../)+learnstack` link, with or without a trailing
+                  # path. The links are validated locally on the developer's
+                  # workstation.
+                  if [[ "$link" =~ ^(\.\./)+learnstack(/|$) ]]; then
                       continue
                   fi
                   link_path="${link%%#*}"