fix(browser): allow fixture to override maxColumns and maxNestedDepth

[SparshM8]

Description

Resolves #218.

This PR updates the FixtureExpect schema and the validateRowShape logic to respect maxColumns and maxNestedDepth overrides. Previously, the browser verify step strictly hardcoded the caps to 12 columns and a nesting depth of 1, which caused legitimate spreadsheet-export adapters to fail CI.

By adding these options, adapter authors can now explicitly permit wider rows or deeper nesting in their verify/<cmd>.json expectations without disabling shape validation entirely.

Related issue: #218

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

• 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

N/A - CLI output remains the same, but adapters with wide rows will now pass webcmd browser verify without throwing shape errors.

[github-actions]

🟠 Maintainer review suggested — low confidence

The automated review could not reach a fully supported conclusion.

Limitations

• Some automated findings could not be verified against the pull request diff.

This review is advisory and does not block merging.