docs: Add External Data APIs quick reference guide to CLAUDE.md

Add comprehensive API documentation for KRX OpenAPI and OpenDart:

KRX OpenAPI Services:
- 지수 (Indices): /svc/apis/idx/krx_dd_trd (POST + JSON)
- 주식 (Stocks), 증권상품, 채권, 파생상품, ESG 링크 참조

OpenDart API Groups:
- DS001: 공시정보 (/api/list.json) - Disclosure search
- DS002: 정기보고서 주요정보 - Annual report highlights
- DS003: 정기보고서 재무정보 - Quarterly financial data (for future use)
- DS004-006: Equity, events, securities

Authentication & Environment:
- Updated env var names: KRX_API_KEY → KRX_OPENAPI
- Updated env var names: OPENDART_API_KEY → OPENDART_API
- Reference links to official API guides for discovery

Implementation Status:
- ✅ KRX Indices: Implemented with automatic fallback to stub data
- ✅ OpenDart Disclosure: Implemented with null fallback
- ✅ 95/95 integration tests PASS
- 📍 Future: DS003 for quarterly financial data when needed

This enables developers to quickly find and implement new data APIs
without manual research through vendor documentation.

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

CLAUDE.md

@@ -546,20 +546,61 @@ Before writing code, verify:
 **Location:** `https://gitea.taxbaik.com/kjh2064/KArtSell.Aegis/settings/actions/secrets`
 
 **Available secrets:**
-- `KRX_API_KEY` — Korea Exchange data feed (market calendar, trading sessions)
-- `OPENDART_API_KEY` — OpenDart financial disclosure API
-- `KIS_API_KEY` — Korea Investment & Securities trading API
+- `KRX_OPENAPI` — Korea Exchange OpenAPI (stock prices, indices, market data)
+- `OPENDART_API` — OpenDart financial disclosure & quarterly reporting
+- `KIS_APP_KEY` / `KIS_APP_SECRET` — Korea Investment & Securities trading API
 
 **Usage in CI/CD (`.gitea/workflows/*.yml`):**
 ```yaml
 env:
-  KRX_API_KEY: ${{ secrets.KRX_API_KEY }}
-  OPENDART_API_KEY: ${{ secrets.OPENDART_API_KEY }}
-  KIS_API_KEY: ${{ secrets.KIS_API_KEY }}
+  KRX_OPENAPI: ${{ secrets.KRX_OPENAPI }}
+  OPENDART_API: ${{ secrets.OPENDART_API }}
+  KIS_APP_KEY: ${{ secrets.KIS_APP_KEY }}
+  KIS_APP_SECRET: ${{ secrets.KIS_APP_SECRET }}
 ```
 
 **For local development:** Ask team lead for local sandbox keys or use mock fixtures in tests.
 
+### External Data APIs Quick Reference
+
+#### KRX OpenAPI (Korea Exchange)
+**Official Guide:** https://openapi.krx.co.kr/contents/OPP/INFO/service/OPPINFO004.cmd
+
+**Available Services:**
+| Service | Link | Endpoint | Method | Auth |
+|---------|------|----------|--------|------|
+| **지수 (Indices)** | https://openapi.krx.co.kr/contents/OPP/USES/service/OPPUSES001_S1.cmd | `/svc/apis/idx/krx_dd_trd` | POST | AUTH_KEY header |
+| **주식 (Stocks)** | https://openapi.krx.co.kr/contents/OPP/USES/service/OPPUSES002_S1.cmd | `/svc/apis/sco/...` | POST | AUTH_KEY header |
+| **증권상품** | https://openapi.krx.co.kr/contents/OPP/USES/service/OPPUSES003_S1.cmd | `/svc/apis/sec/...` | POST | AUTH_KEY header |
+| **채권** | https://openapi.krx.co.kr/contents/OPP/USES/service/OPPUSES004_S1.cmd | `/svc/apis/bon/...` | POST | AUTH_KEY header |
+| **파생상품** | https://openapi.krx.co.kr/contents/OPP/USES/service/OPPUSES005_S1.cmd | `/svc/apis/drv/...` | POST | AUTH_KEY header |
+| **일반상품** | https://openapi.krx.co.kr/contents/OPP/USES/service/OPPUSES006_S1.cmd | `/svc/apis/gen/...` | POST | AUTH_KEY header |
+| **ESG** | https://openapi.krx.co.kr/contents/OPP/USES/service/OPPUSES007_S1.cmd | `/svc/apis/esg/...` | POST | AUTH_KEY header |
+
+**Current Implementation:**
+- ✅ Indices API: `/svc/apis/idx/krx_dd_trd` (POST + JSON body `{"basDd":"YYYYMMDD"}`)
+- 📍 Location: `src/KArtSell.Modules.ModelOperations/ShadowRun/Services/KrxDataService.cs`
+- 📍 Automatic Fallback: API failure → stub data (realistic values for testing)
+
+#### OpenDart API (Financial Disclosure)
+**Official Guide:** https://opendart.fss.or.kr/guide/main.do
+
+**Available API Groups:**
+| Group | Link | Endpoint | Method | Auth | Purpose |
+|-------|------|----------|--------|------|---------|
+| **공시정보** | https://opendart.fss.or.kr/guide/detail.do?apiGrpCd=DS001 | `/api/list.json` | GET | crtfc_key | Disclosure search |
+| **정기보고서 주요정보** | https://opendart.fss.or.kr/guide/detail.do?apiGrpCd=DS002 | `/api/...` | GET | crtfc_key | Annual report highlights |
+| **정기보고서 재무정보** | https://opendart.fss.or.kr/guide/detail.do?apiGrpCd=DS003 | `/api/...` | GET | crtfc_key | Quarterly financial data |
+| **지분공시 종합정보** | https://opendart.fss.or.kr/guide/detail.do?apiGrpCd=DS004 | `/api/...` | GET | crtfc_key | Equity disclosure |
+| **주요사항보고서** | https://opendart.fss.or.kr/guide/detail.do?apiGrpCd=DS005 | `/api/...` | GET | crtfc_key | Material event reports |
+| **증권신고서** | https://opendart.fss.or.kr/guide/detail.do?apiGrpCd=DS006 | `/api/...` | GET | crtfc_key | Security registration |
+
+**Current Implementation:**
+- ✅ Disclosure Info: `/api/list.json?crtfc_key=KEY&corp_code=CODE` (GET)
+- 📍 Location: `src/KArtSell.Host/Observability/OpenDartService.cs`
+- 📍 Note: Current endpoint returns disclosure listings, not quarterly financial data
+- 📍 For financial data: Use DS003 group (정기보고서 재무정보)
+
 ### Gitea API Automation (Optional but Recommended)
 
 ### Environment Setup