Improve vp install GitHub Actions error output so failures are obvious immediately #51

Summary

When vp install fails in GitHub Actions, the action output should surface the actual cause immediately and prominently.

Right now the failure mode can be too opaque. One example is when the lockfile is out of date, where the useful error is easy to miss in the Actions log output.

Problem

In CI, people scan logs fast. If vp install prints a lot of wrapper/action output before the real package manager error is obvious, users spend too long figuring out what actually broke.

Example cases

• lockfile is not up to date
• auth token missing
• registry misconfiguration
• package manager install step exits with a known common failure

Expected behavior

If vp install fails, the action should make the root cause immediately visible in GitHub Actions, ideally by:

• emitting a concise top-level error summary
• highlighting the underlying package manager error near the end of the log
• using GitHub Actions error annotations when possible
• mapping common failure modes to clearer messages

Why this matters

The current experience makes routine CI failures harder to debug than they should be. For common mistakes like an outdated lockfile, the action should basically point a big arrow at the real issue.

Suggested direction

Even a small wrapper improvement would help a lot, for example:

• detect known pnpm/npm install failures
• print a short human-readable diagnosis
• preserve the raw underlying output below it for debugging