fix(ci): commit site/pnpm-lock.yaml so deploy-docs can cache

The deploy-docs workflow's pnpm cache step resolves
site/pnpm-lock.yaml, which wasn't committed — the Starlight
scaffold landed without it. Workflow failed on main after
f3cb69f with 'Some specified paths were not resolved, unable
to cache dependencies.' Commit the lockfile and add .astro/
to .gitignore so subsequent runs don't drag build cache in.

Author: zakelfassi

.gitignore

@@ -12,6 +12,7 @@ yarn-error.log*
 dist/
 build/
 *.tsbuildinfo
+.astro/
 
 # Environment & secrets
 .env