fix(sources): use shared yamlEscape in blog release frontmatter

[oritwoen]

Description

formatBlogRelease was doing its own YAML escaping for the title field (only double quotes), and emitting version and url completely raw. Blog post titles with backslashes or newlines corrupt the frontmatter, and URLs with # fragments could get truncated as YAML comments depending on whitespace.

Third instance of the same bug class, after buildFrontmatter (#34) and formatRelease (#37).

Linked Issues

Related to #34, #37

Additional context

One-file change, function is internal and not exported. Typecheck clean.