docs: update CLAUDE.md with DCL parser information

- Add ADIF Parser utility section (src/backend/utils/adif-parser.js)
- Add DCL Service section with API integration details
- Update Confirmation Systems section with DCL information
- Add ADIF Format section explaining field format and DCL-specific fields
- Update Recent Commits with DCL parser implementation

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

CLAUDE.md

@@ -163,6 +163,20 @@ The award system is JSON-driven and located in `award-definitions/` directory. E
 - Add new awards by creating JSON definition files
 - Add filename to `loadAwardDefinitions()` file list in awards.service.js
 
+**ADIF Parser**: `src/backend/utils/adif-parser.js`
+- `parseADIF(adifData)`: Parse ADIF format into QSO records
+- `parseDCLResponse(response)`: Parse DCL's JSON response format `{ "adif": "..." }`
+- `normalizeBand(band)`: Standardize band names (80m, 40m, etc.)
+- `normalizeMode(mode)`: Standardize mode names (CW, FT8, SSB, etc.)
+- Used by both LoTW and DCL services for consistency
+
+**DCL Service**: `src/backend/services/dcl.service.js`
+- `fetchQSOsFromDCL(dclApiKey, sinceDate)`: Fetch from DCL API
+- `parseDCLJSONResponse(jsonResponse)`: Parse example/test payloads
+- `syncQSOs(userId, dclApiKey, sinceDate, jobId)`: Sync QSOs to database
+- `getLastDCLQSLDate(userId)`: Get last QSL date for incremental sync
+- Ready for when DCL publishes their API
+
 ### DLD Award Implementation (COMPLETED)
 
 The DLD (Deutschland Diplom) award was recently implemented:
@@ -215,15 +229,43 @@ To add a new award:
 ### Confirmation Systems
 
 - **LoTW (Logbook of The World)**: ARRL's confirmation system
+  - Service: `src/backend/services/lotw.service.js`
   - Fields: `lotwQslRstatus`, `lotwQslRdate`
   - Used for DXCC, WAS, VUCC, most awards
+  - ADIF format with `<EOR>` delimiters
+  - Supports incremental sync by date
 
 - **DCL (DARC Community Logbook)**: DARC's confirmation system
+  - Service: `src/backend/services/dcl.service.js`
   - Fields: `dclQslRstatus`, `dclQslRdate`
+  - DOK fields: `darcDok` (partner's DOK), `myDarcDok` (user's DOK)
   - Required for DLD award
   - German amateur radio specific
+  - API in development (parser ready)
+  - Response format: JSON with ADIF string in `adif` field
+  - Supports DOK (DARC Ortsverband Kennung) data
+
+### ADIF Format
+
+Both LoTW and DCL return data in ADIF (Amateur Data Interchange Format):
+- Field format: `<FIELD_NAME:length>value`
+- Record delimiter: `<EOR>` (end of record)
+- Header ends with: `<EOH>` (end of header)
+- Example: `<CALL:5>DK0MU<BAND:3>80m<QSO_DATE:8>20250621<EOR>`
+
+**DCL-specific fields**:
+- `DCL_QSL_RCVD`: DCL confirmation status (Y/N/?)
+- `DCL_QSLRDATE`: DCL confirmation date (YYYYMMDD)
+- `DARC_DOK`: QSO partner's DOK
+- `MY_DARC_DOK`: User's own DOK
+- `STATION_CALLSIGN`: User's callsign
 
 ### Recent Commits
 
+- `8a1a580`: feat: implement DCL ADIF parser and service integration
+  - Add shared ADIF parser utility (src/backend/utils/adif-parser.js)
+  - Implement DCL service with API integration ready
+  - Refactor LoTW service to use shared parser
+  - Tested with example DCL payload (6 QSOs parsed successfully)
 - `c982dcd`: feat: implement DLD (Deutschland Diplom) award
 - `322ccaf`: docs: add DLD (Deutschland Diplom) award documentation