Add Copilot Workshops sync workflow + Learning Hub i18n (#2325)

Adds an agentic (gh-aw) workflow that mirrors the multi-harness workshop
from github-samples/copilot-workshops into the Learning Hub, plus the
Starlight infrastructure it needs: GitHub-admonition rendering, i18n
locales with English at the site root, and a language picker that only
appears when a page has a non-English translation.


Copilot-Session: 9e1d1a4c-a422-4cae-8ea7-b3d5171f58e3

Co-authored-by: GeekTrainer <GeekTrainer@users.noreply.github.com>
Co-authored-by: Copilot App <223556219+Copilot@users.noreply.github.com>

website/package.json

@@ -28,6 +28,7 @@
     "isomorphic-dompurify": "^2.36.0",
     "jszip": "^3.10.1",
     "marked": "^18.0.2",
+    "remark-github-admonitions-to-directives": "^2.1.0",
     "shiki": "^4.0.2"
   },
   "devDependencies": {