Task: Switch to `pnpm` for JS dep management

[nlebovits]

Describe the task

We are currently using npm for dependency management for FE development. Although this works, pnpm is now the preferred package manager for working with Vercel (which we do), and is generally more robust and faster than npm. Switch over our dependency management to use pnpm instead of npm, updating all documentation as necessary and flagging any issues that arise.