Use pnpm for the UI workflow

[amirgholipour]

What changed

• Declare pnpm as the UI package manager.
• Replace the npm lockfile with pnpm-lock.yaml.
• Use frozen pnpm installs in the deployment script and UI container build.
• Update current UI development and build documentation.

Why this change is proposed

The UI workflow currently mixes an npm lockfile with installation commands that can rewrite dependency resolution during deployment. A single declared package manager and frozen lockfile make local, CI, and container installs deterministic.

This proposal standardizes the current UI on pnpm while leaving the Python and infrastructure package workflows unchanged.

Benefits

• Reproducible UI dependency resolution across development and deployment.
• Faster installs and better package-store reuse.
• A container build that fails clearly when the lockfile and manifest diverge.
• One documented command set for the current UI.

Validation

• Generated the lockfile from the current upstream UI manifest.
• Verified frozen-lockfile resolution.
• Verified the current production UI build completes with pnpm.
• Reviewed the branch against the current upstream main.

Authored by Saeed Kasmani (amirgholipour).