fix(ci): commit pnpm-lock.yaml and remove it from .gitignore

CI workflows use --frozen-lockfile and cache: pnpm, both of which require
pnpm-lock.yaml to be present in the repository. Removing it from .gitignore
and committing it enables reproducible installs in CI.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: ralyodio

.gitignore

@@ -34,5 +34,4 @@ yarn-error.log*
 next-env.d.ts
 
 # pnpm
-pnpm-lock.yaml
 package-lock.json