fix(core): bypass poisoned markdown cache

[1052326311]

Issue for this PR

Closes #42350

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

It bypasses gray-matter's content cache in the shared markdown parser. Without this, a strict YAML error caches the original content before the sanitized retry, so parsing the same skill again returns empty frontmatter. Passing an options object disables that cache while preserving the existing strict-then-sanitize behavior.

How did you verify your code works?

On current origin/dev (e23586af2623f1bc2e8e6965d2d7acf7bd03d5c3), the issue's content returns sanitized data once and {} on the second parse. On candidate 80169062af83bead2f28b7a2046815daf38e8ccf, both parses return the sanitized data.

• Focused regression: 1 pass, 2 assertions
• Package and repository typechecks: pass (30/30 root tasks)
• Oxlint and Prettier checks on changed files: pass

Screenshots / recordings

Not applicable; this is a parser fix.

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR

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