feat: skip QSOs with unchanged confirmation data

When syncing from LoTW/DCL, only update QSOs if confirmation data
has changed. This avoids unnecessary database updates and makes it
clear which QSOs actually changed.

- LoTW: Checks if lotwQslRstatus or lotwQslRdate changed
- DCL: Checks if dclQslRstatus, dclQslRdate, DOK, or grid changed
- Frontend: Shows skipped count in sync summary

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

src/backend/services/lotw.service.js

@@ -222,6 +222,7 @@ export async function syncQSOs(userId, lotwUsername, lotwPassword, sinceDate = n
 
   let addedCount = 0;
   let updatedCount = 0;
+  let skippedCount = 0;
   const errors = [];
   const addedQSOs = [];
   const updatedQSOs = [];
@@ -247,22 +248,34 @@ export async function syncQSOs(userId, lotwUsername, lotwPassword, sinceDate = n
         .limit(1);
 
       if (existing.length > 0) {
-        await db
-          .update(qsos)
-          .set({
-            lotwQslRdate: dbQSO.lotwQslRdate,
-            lotwQslRstatus: dbQSO.lotwQslRstatus,
-            lotwSyncedAt: dbQSO.lotwSyncedAt,
-          })
-          .where(eq(qsos.id, existing[0].id));
-        updatedCount++;
-        // Track updated QSO (CALL and DATE)
-        updatedQSOs.push({
-          callsign: dbQSO.callsign,
-          date: dbQSO.qsoDate,
-          band: dbQSO.band,
-          mode: dbQSO.mode,
-        });
+        const existingQSO = existing[0];
+
+        // Check if LoTW confirmation data has changed
+        const confirmationChanged =
+          existingQSO.lotwQslRstatus !== dbQSO.lotwQslRstatus ||
+          existingQSO.lotwQslRdate !== dbQSO.lotwQslRdate;
+
+        if (confirmationChanged) {
+          await db
+            .update(qsos)
+            .set({
+              lotwQslRdate: dbQSO.lotwQslRdate,
+              lotwQslRstatus: dbQSO.lotwQslRstatus,
+              lotwSyncedAt: dbQSO.lotwSyncedAt,
+            })
+            .where(eq(qsos.id, existingQSO.id));
+          updatedCount++;
+          // Track updated QSO (CALL and DATE)
+          updatedQSOs.push({
+            callsign: dbQSO.callsign,
+            date: dbQSO.qsoDate,
+            band: dbQSO.band,
+            mode: dbQSO.mode,
+          });
+        } else {
+          // Skip - same data
+          skippedCount++;
+        }
       } else {
         await db.insert(qsos).values(dbQSO);
         addedCount++;
@@ -288,13 +301,14 @@ export async function syncQSOs(userId, lotwUsername, lotwPassword, sinceDate = n
     }
   }
 
-  logger.info('LoTW sync completed', { total: adifQSOs.length, added: addedCount, updated: updatedCount, jobId });
+  logger.info('LoTW sync completed', { total: adifQSOs.length, added: addedCount, updated: updatedCount, skipped: skippedCount, jobId });
 
   return {
     success: true,
     total: adifQSOs.length,
     added: addedCount,
     updated: updatedCount,
+    skipped: skippedCount,
     addedQSOs,
     updatedQSOs,
     errors: errors.length > 0 ? errors : undefined,