fix(hosted): accept expiresAt in browser run responses

[rishabhraj36]

Description

Updates the hosted browser response contract and runtime validation to accept the optional run.expiresAt timestamp returned by Webcmd Cloud.

Previously, the strict response validator rejected otherwise-valid cloud responses containing this field, causing hosted browser commands and cloud-backed evals to fail with an invalid browser run response error.

Adds regression coverage to ensure:

• String-valued expiresAt fields are accepted.
• Responses without expiresAt remain supported.
• Non-string expiresAt values are rejected.

Related issue: Closes #193

Type of Change

• 🐛 Bug fix
• ✨ New feature
• 🌐 New site adapter
• 📝 Documentation
• ♻️ Refactor
• 🔧 CI / build / tooling

Checklist

• I ran the checks relevant to this PR
• I updated tests or docs if needed
• I included output or screenshots when useful

Adapter Notes

Not applicable—this change does not modify a site adapter or command interface.

• Updated generated or lean docs when command discoverability changed
• Used positional args for the command's primary subject unless a named flag is clearly better
• Normalized expected adapter failures to CliError subclasses instead of raw Error

Screenshots / Output

Before:

Webcmd Cloud returned an invalid browser run response.

[github-actions]

🟢 No documentation gap found — medium confidence

The automated review found no documentation gap in the supplied changes.

This review is advisory and does not block merging.