Docs idea: add a small RAG failure mode checklist for Verba users

Hi Verba maintainers, thank you.

Suggestion Add a small “RAG failure mode checklist” section to help users understand common failure patterns in RAG apps.

What it includes

• typical symptoms users see
• map each to a stable failure-mode code (16 codes)
• minimal first checks and fixes

Reference taxonomy WFGY Problem Map (No 1 to No 16): https://github.com/onestardao/WFGY/blob/main/ProblemMap/README.md

Scope Docs-only. If you want, I can draft it and open a PR.