fix(scorer): report invalid schema patterns

[vsolano9]

What & why

Convert an invalid user-supplied JSON Schema pattern from an uncaught SyntaxError into a normal failing scorer result. The error now includes the exact JSON path, pattern, and runtime compilation message, so one malformed schema cannot abort the entire eval run.

Closes #8

Changes

• catch regex compilation failures inside validate()
• append a path-attributed validation error for invalid patterns
• cover a nested $.account invalid pattern through the real scorer
• pin the neighboring valid-pattern mismatch message

Validation

• npm run typecheck
• npm run lint
• npm run build
• npm test — 9 files, 70 tests passed
• focused invalid/mismatch coverage repeated 20 times
• built-validator nested-path proof
• deterministic 7-case example suite passed
• full typecheck/lint/build/test/example gate passed on Node 20.20.2 and 22.23.2
• npm pack --dry-run and clean installed-tarball public validateJsonSchema smoke passed
• production dependency audit reports zero findings
• git diff --check

Checklist

• Focused change with a clear description
• Ran the complete documented local gate
• No network or API-key test path
• No dependency, public API, or configuration change
• Linked issue with Closes #8

Notes

Fresh install reports seven existing development-dependency advisories; production dependencies report zero, and this PR changes neither manifest nor lockfile.

[github-actions]

Welcome, @vsolano9, and thanks for your first pull request to Evalgate.

A quick look at CONTRIBUTING.md covers how things are set up and run here.

I'll review this shortly. Ask anything in the thread if something is unclear.

[vsolano9]

Postflight note on the red quality-gate context:

• The quality comparison itself passed: base 94.2% -> head 94.2% (0.0pp) and No regressions beyond tolerance.
• The action then exited 2 only while publishing its optional PR comment: [evalgate] failed to create comment (403). Fork-triggered pull_request runs receive a read-only token even though the workflow requests pull-requests: write.
• The separate repository CI completed successfully on Node 20 and 22, including typecheck, lint, build, all 70 tests, and the example-suite smoke.

This PR does not change the action or workflow; the failing context is the existing fork-comment permission path, not a scorer/test regression.