ui: Explicitly set pnpm version to enable vercel builds

[manojVivek]

No description provided.

[alwaysmeticulous]

🤖 Meticulous evaluated 60 user flows and took 364 visual snapshots. Meticulous has not yet run on a3581fc of the main branch and so there was nothing to compare against.

If you recently setup Meticulous, this is expected. Meticulous will start reporting comparisons for new pull requests after the next commit to the main branch.

_{Last updated for commit 149cfe9. This comment will update as new commits are pushed.}