feat: add LoTW sync type support (QSL/QSO delta/full)

- Add syncType parameter to LoTW sync: 'qsl_delta', 'qsl_full', 'qso_delta', 'qso_full'
- qsl_* = only confirmed QSOs (qso_qsl=yes)
- qso_* = all QSOs confirmed+unconfirmed (qso_qsl=no)
- delta = incremental sync with date filter
- full = sync all records without date filter
- Add getLastLoTWQSODate() for QSO-based incremental sync
- Add sync type dropdown selector on QSO page
- Update job queue service to handle sync types
- Update API endpoint to accept syncType in request body

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

src/backend/index.js

@@ -314,8 +314,9 @@ const app = new Elysia()
    * POST /api/lotw/sync
    * Queue a LoTW sync job (requires authentication)
    * Returns immediately with job ID
+   * Body: { syncType?: 'qsl_delta' | 'qsl_full' | 'qso_delta' | 'qso_full' }
    */
-  .post('/api/lotw/sync', async ({ user, set }) => {
+  .post('/api/lotw/sync', async ({ user, body, set }) => {
     if (!user) {
       logger.warn('/api/lotw/sync: Unauthorized access attempt');
       set.status = 401;
@@ -323,7 +324,8 @@ const app = new Elysia()
     }
 
     try {
-      const result = await enqueueJob(user.id, 'lotw_sync');
+      const { syncType = 'qsl_delta' } = body || {};
+      const result = await enqueueJob(user.id, 'lotw_sync', { syncType });
 
       if (!result.success && result.existingJob) {
         return {