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/dcl.service.js

@@ -192,6 +192,7 @@ export async function syncQSOs(userId, dclApiKey, sinceDate = null, jobId = null
 
     let addedCount = 0;
     let updatedCount = 0;
+    let skippedCount = 0;
     const errors = [];
     const addedQSOs = [];
     const updatedQSOs = [];
@@ -219,26 +220,41 @@ export async function syncQSOs(userId, dclApiKey, sinceDate = null, jobId = null
           .limit(1);
 
         if (existing.length > 0) {
-          // Update existing QSO with DCL confirmation and DOK data
-          await db
-            .update(qsos)
-            .set({
-              dclQslRdate: dbQSO.dclQslRdate,
-              dclQslRstatus: dbQSO.dclQslRstatus,
-              darcDok: dbQSO.darcDok || existing[0].darcDok,
-              myDarcDok: dbQSO.myDarcDok || existing[0].myDarcDok,
-              grid: dbQSO.grid || existing[0].grid,
-              gridSource: dbQSO.gridSource || existing[0].gridSource,
-            })
-            .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 DCL confirmation or DOK data has changed
+          const dataChanged =
+            existingQSO.dclQslRstatus !== dbQSO.dclQslRstatus ||
+            existingQSO.dclQslRdate !== dbQSO.dclQslRdate ||
+            existingQSO.darcDok !== (dbQSO.darcDok || existingQSO.darcDok) ||
+            existingQSO.myDarcDok !== (dbQSO.myDarcDok || existingQSO.myDarcDok) ||
+            existingQSO.grid !== (dbQSO.grid || existingQSO.grid);
+
+          if (dataChanged) {
+            // Update existing QSO with changed DCL confirmation and DOK data
+            await db
+              .update(qsos)
+              .set({
+                dclQslRdate: dbQSO.dclQslRdate,
+                dclQslRstatus: dbQSO.dclQslRstatus,
+                darcDok: dbQSO.darcDok || existingQSO.darcDok,
+                myDarcDok: dbQSO.myDarcDok || existingQSO.myDarcDok,
+                grid: dbQSO.grid || existingQSO.grid,
+                gridSource: dbQSO.gridSource || existingQSO.gridSource,
+              })
+              .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 {
           // Insert new QSO
           await db.insert(qsos).values(dbQSO);
@@ -274,6 +290,7 @@ export async function syncQSOs(userId, dclApiKey, sinceDate = null, jobId = null
       total: adifQSOs.length,
       added: addedCount,
       updated: updatedCount,
+      skipped: skippedCount,
       addedQSOs,
       updatedQSOs,
       confirmed: adifQSOs.filter(q => q.dcl_qsl_rcvd === 'Y').length,