fix: audit findings in src/memory

[avoidwork]

Code Audit: memory

Summary

Total issues: 1 (critical: 0, high: 0, medium: 1, low: 0)

One medium-severity bug found in the writer module related to YAML frontmatter string escaping.

Findings

File	Issue Type	Severity	Summary
src/memory/writer.js	bug	medium	String values in frontmatter are not escaped, which could cause YAML parsing errors if the string contains quotes or newlines

Remediation Priority

1. [Medium severity bugs]
   • Escape string values in frontmatter to prevent YAML parsing errors (lines 27-35 in writer.js)

[avoidwork]

Fixed in #346.