docs(fb-40): rag-v2 prompt + README + design + SKILL + INDEX

- README: [rag] prompt_template_version default rag-v2 + V2 강화 3 규칙
- design §7: rag-v2 본문 + V1 legacy note
- SKILL.md: mcp__kebab__ask 응답 행태 변화 안내
- task spec: status open → completed, design + plan 링크
- INDEX: fb-40 ✅ 머지 (2026-05-10)

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

integrations/claude-code/kebab/SKILL.md

@@ -72,6 +72,7 @@ Input:
 - Returns `answer.v1`: `answer` (markdown), `citations[]`, `grounded` (bool), `refusal_reason`, `model`, `conversation_id`, `turn_index`.
 - **If `grounded == false`** → KB doesn't have enough context. Don't paraphrase the refusal as if it were an answer. Tell the user the KB came up dry and fall back to your own knowledge or ask for the source.
 - For follow-up turns on the same topic, pass `session_id` (e.g. `"team-onboarding-2026-05"`) and reuse it across the conversation. Sessions persist until `kebab reset --data-only`.
+- p9-fb-40: 기본 `prompt_template_version = "rag-v2"`. 답변이 더 strict — fact 인용 시 verbatim span, 학습 지식 동원 금지, 근거 모호 시 "확실하지 않다" 출현 가능. user 가 `[rag] prompt_template_version = "rag-v1"` 명시 시 legacy 동작.
 
 ### `mcp__kebab__fetch` — when you need raw text