chore: update deps to latest; serialize Pages deployments

astro 7.1.6 -> 7.2.1 and refresh the lockfile, which pulls nanoid 3.3.18
and clears the open Dependabot advisory. mdx/tailwind were already latest.
Verified with a clean local build.

Add a `pages` concurrency group so a queued run waits instead of failing
against an in-progress deployment.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

Author: aliencaocao

.github/workflows/deploy.yml

@@ -10,6 +10,12 @@ permissions:
   pages: write
   id-token: write
 
+# Allow one deployment at a time; queued runs wait instead of failing on an
+# in-progress deployment.
+concurrency:
+  group: pages
+  cancel-in-progress: false
+
 jobs:
   build:
     runs-on: ubuntu-latest