fix: add missing timeOn field to LoTW duplicate detection

Critical bug: LoTW sync was missing timeOn in the duplicate detection
query, causing multiple QSOs with the same callsign/date/band/mode
but different times to be treated as duplicates.

Example: If you worked DL1ABC on 2025-01-15 at 10:00, 12:00, and 14:00
all on 80m CW, only the first QSO would be imported.

Now matches DCL sync logic which correctly includes timeOn:
- userId, callsign, qsoDate, timeOn, band, mode

This ensures all unique QSOs are properly imported from LoTW.

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

src/backend/services/lotw.service.js

@@ -241,6 +241,7 @@ export async function syncQSOs(userId, lotwUsername, lotwPassword, sinceDate = n
             eq(qsos.userId, userId),
             eq(qsos.callsign, dbQSO.callsign),
             eq(qsos.qsoDate, dbQSO.qsoDate),
+            eq(qsos.timeOn, dbQSO.timeOn),
             eq(qsos.band, dbQSO.band),
             eq(qsos.mode, dbQSO.mode)
           )