feat(markdown): render frontmatter in file previews - #8202

💭 I'm checking the new markdownFrontmatter.ts file for import compliance—using proper namespace imports for Effect Schema and Option, and a named import for a pure schema helper, which is fine. Now I'm looking at whether calling Schema.encodeSync at module scope violates the pattern. No Effect services are created or consumed in this file, so the convention check likely has no findings here, but I want to quickly glance at fromYaml's signature just to be thorough even though correctness isn't strictly in scope.

1. git_tools — fromYaml

2. browse_code — packages/client-runtime/src/markdownFrontmatter.ts

💭 No Effect services are touched and imports follow conventions, so there are no violations to report. I need to reconcile the instruction to output exactly "All clear" with the requirement to produce structured JSON — I'll set the title/summary fields to "All clear" while still satisfying the schema, treating the check as passing since there are no findings.