📝 docs: comprehensive MCP usage guide (fb-31)

신규 docs/mcp-usage.md (~280 line) — agent integration 의 종합 가이드:

- Quick start + `--config` thread 예시
- Host config 예시 (Claude Code / Cursor / OpenAI Agents / Copilot CLI)
- 6 tool catalog (search / ask / schema / doctor / ingest_file / ingest_stdin)
  각 tool 의 input shape, defaults, output 예시, "언제 사용", mutation
  주의사항.
- Troubleshooting — error.v1 의 7 code 별 조치 표 + grounded:false +
  doctor !ok + empty search + tool-not-found 시나리오.
- Multi-turn ask + session 관리 — session_id 명명, 새 session 시작
  시점, lifetime, single-shot vs session 비교.
- Performance / Security 절.

README.md 의 기존 MCP 절은 quick start 만 유지하고 docs/mcp-usage.md
링크. integrations/claude-code/kebab/SKILL.md 도 동일 cross-link.

agent 사용자 도그푸딩 후속 의견 — host-agnostic 가이드 + 명시적
troubleshooting 표 + multi-turn session 명명 컨벤션 부재 해소.

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

integrations/claude-code/kebab/SKILL.md

@@ -90,6 +90,8 @@ Claude Code spawns `kebab mcp` at session start; the process stays alive across
 
 If your host doesn't support MCP, the CLI subprocess pattern (`kebab search --json` / `kebab ask --json`) above continues to work.
 
+For per-tool input/output examples, error code reference, multi-turn ask + session management, and host config beyond Claude Code (Cursor / OpenAI Agents / Copilot CLI), see [docs/mcp-usage.md](../../../docs/mcp-usage.md) in the kebab repo.
+
 ## Recipe D — agent fetched a web doc, save to KB
 
 When you've fetched a markdown article (e.g. via WebFetch) that the user might query later: