Re-enable complete build on vercel

[richadr]

Due to OOM-errors and other issues that only appeared on Vercel, a build:vercel command was temporarily added to circumvent this.

On 20260106 the build pipeline was upgraded and this should not be needed anymore.

Acceptance criteria

• verified that the build command on vercel works
• vercel configured to run the build command
• build:vercel command removed from package.json