fix(memory): tighten memory recall fallback guidance

[dommonkhouse]

Summary

• broaden memory-recall trigger guidance for substantive tasks
• add guidance for exact failure phrase searches and vector-service fallback handling
• document a generic raw markdown fallback search without user-specific paths

Verification

• git diff --check origin/main..HEAD
• scanned diff additions for user-specific local paths

[dommonkhouse]

Ready for maintainer review and merge. I verified this PR is non-draft, mergeable, and has no configured checks reporting failures.