fix(post-compaction-audit): RegExp .source leaks raw regex syntax in audit warning #22339
Description
When the post-compaction audit fires for a missing regex entry, the warning displays raw .source output instead of a readable pattern.
Actual: memory\/\d{4}-\d{2}-\d{2}\.md
Expected: memory/YYYY-MM-DD.md
Root cause: missingPatterns.push(required.source) in post-compaction-audit.ts. In practice the raw regex escapes caused the audit message to be mistaken for a prompt injection attempt.
Suggested fix: derive a readable label from the pattern or add an optional label field to DEFAULT_REQUIRED_READS entries.
Related: #21957 / PR #22124. WORKFLOW_AUTO.md is covered there — this is a separate display-only bug