feat: add QSO page filters and fix DXCC entity priority

- Add confirmation type filter (LoTW Only, DCL Only, Both, None)
- Add search box for callsign, entity, and grid square
- Rename "All Confirmation" to "All QSOs" for clarity
- Fix exclusive filter logic using separate SQL conditions
- Add debug logging for filter troubleshooting
- Implement DXCC priority: LoTW > DCL
- Document QSO page filters and DXCC handling in CLAUDE.md

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

CLAUDE.md

@@ -467,3 +467,82 @@ Both LoTW and DCL return data in ADIF (Amateur Data Interchange Format):
 - LoTW never sends DOK data; only DCL provides DOK fields
 
 **Important**: DCL sync only updates DOK/grid fields when DCL provides non-empty values. This prevents accidentally clearing DOK data that was manually entered or imported from other sources.
+
+### QSO Page Filters
+
+The QSO page (`src/frontend/src/routes/qsos/+page.svelte`) includes advanced filtering capabilities:
+
+**Available Filters**:
+- **Search Box**: Full-text search across callsign, entity (DXCC country), and grid square fields
+  - Press Enter to apply search
+  - Case-insensitive partial matching
+- **Band Filter**: Dropdown to filter by amateur band (160m, 80m, 60m, 40m, 30m, 20m, 17m, 15m, 12m, 10m, 6m, 2m, 70cm)
+- **Mode Filter**: Dropdown to filter by mode (CW, SSB, AM, FM, RTTY, PSK31, FT8, FT4, JT65, JT9)
+- **Confirmation Type Filter**: Filter by confirmation status
+  - "All QSOs": Shows all QSOs (no filter)
+  - "LoTW Only": Shows QSOs confirmed by LoTW but NOT DCL
+  - "DCL Only": Shows QSOs confirmed by DCL but NOT LoTW
+  - "Both Confirmed": Shows QSOs confirmed by BOTH LoTW AND DCL
+  - "Not Confirmed": Shows QSOs confirmed by NEITHER LoTW nor DCL
+- **Clear Button**: Resets all filters and reloads all QSOs
+
+**Backend Implementation** (`src/backend/services/lotw.service.js`):
+- `getUserQSOs(userId, filters, options)`: Main filtering function
+- Supports pagination with `page` and `limit` options
+- Filter logic uses Drizzle ORM query builders for safe SQL generation
+- Debug logging when `LOG_LEVEL=debug` shows applied filters
+
+**Frontend API** (`src/frontend/src/lib/api.js`):
+- `qsosAPI.getAll(filters)`: Fetch QSOs with optional filters
+- Filters passed as query parameters: `?band=20m&mode=CW&confirmationType=lotw&search=DL`
+
+### DXCC Entity Priority Logic
+
+When syncing QSOs from multiple confirmation sources, the system follows a priority order for DXCC entity data:
+
+**Priority Order**: LoTW > DCL
+
+**Implementation** (`src/backend/services/dcl.service.js`):
+```javascript
+// DXCC priority: LoTW > DCL
+// Only update entity fields from DCL if:
+// 1. QSO is NOT LoTW confirmed, AND
+// 2. DCL actually sent entity data, AND
+// 3. Current entity is missing
+const hasLoTWConfirmation = existingQSO.lotwQslRstatus === 'Y';
+const hasDCLData = dbQSO.entity || dbQSO.entityId;
+const missingEntity = !existingQSO.entity || existingQSO.entity === '';
+
+if (!hasLoTWConfirmation && hasDCLData && missingEntity) {
+  // Fill in entity data from DCL (only if DCL provides it)
+  updateData.entity = dbQSO.entity;
+  updateData.entityId = dbQSO.entityId;
+  // ... other entity fields
+}
+```
+
+**Rules**:
+1. **LoTW-confirmed QSOs**: Always use LoTW's DXCC data (most reliable)
+2. **DCL-only QSOs**: Use DCL's DXCC data IF available in ADIF payload
+3. **Empty entity fields**: If DCL doesn't send DXCC data, entity remains empty
+4. **Never overwrite**: Once LoTW confirms with entity data, DCL sync won't change it
+
+**Important Note**: DCL API currently doesn't send DXCC/entity fields in their ADIF export. This is a limitation of the DCL API, not the application. If DCL adds these fields in the future, the system will automatically use them for DCL-only QSOs.
+
+### Recent Development Work (January 2025)
+
+**QSO Page Enhancements**:
+- Added confirmation type filter with exclusive logic (LoTW Only, DCL Only, Both Confirmed, Not Confirmed)
+- Added search box for filtering by callsign, entity, or grid square
+- Renamed "All Confirmation" to "All QSOs" for clarity
+- Fixed filter logic to properly handle exclusive confirmation types
+
+**Bug Fixes**:
+- Fixed confirmation filter showing wrong QSOs (e.g., "LoTW Only" was also showing DCL QSOs)
+- Implemented proper SQL conditions for exclusive filters using separate condition pushes
+- Added debug logging to track filter application
+
+**DXCC Entity Handling**:
+- Clarified that DCL API doesn't send DXCC fields (current limitation)
+- Implemented priority logic: LoTW entity data takes precedence over DCL
+- System ready to auto-use DCL DXCC data if they add it in future API updates