revert: remove LoTW sync type support (QSL/QSO delta/full)

This reverts commit 5b78935 which added:
- Sync type parameter (qsl_delta, qsl_full, qso_delta, qso_full)
- getLastLoTWQSODate() function
- Sync type dropdown on QSO page
- Job queue handling of sync types

Reason: LoTW doesn't provide DXCC entity data for unconfirmed QSOs,
which causes award calculation issues. Going back to QSL-only sync.

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

src/backend/index.js

@@ -314,9 +314,8 @@ 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, body, set }) => {
+  .post('/api/lotw/sync', async ({ user, set }) => {
     if (!user) {
       logger.warn('/api/lotw/sync: Unauthorized access attempt');
       set.status = 401;
@@ -324,8 +323,7 @@ const app = new Elysia()
     }
 
     try {
-      const { syncType = 'qsl_delta' } = body || {};
-      const result = await enqueueJob(user.id, 'lotw_sync', { syncType });
+      const result = await enqueueJob(user.id, 'lotw_sync');
 
       if (!result.success && result.existingJob) {
         return {