fix: return correct count from deleteQSOs function

The db.delete() returns a result object with a 'changes' property
indicating the number of affected rows, not the count directly.

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

src/backend/services/lotw.service.js

@@ -612,7 +612,8 @@ export async function getLastLoTWQSLDate(userId) {
  */
 export async function deleteQSOs(userId) {
   const result = await db.delete(qsos).where(eq(qsos.userId, userId));
-  return result;
+  // Drizzle with SQLite/bun:sqlite returns { changes: number } indicating affected rows
+  return result.changes || 0;
 }
 
 /**