fix: prevent infinite retry loop for auto-sync users without credentials

When auto-sync is enabled but credentials (LoTW/DCL) are removed, the
scheduler would continuously try to sync every minute, logging the same
warning forever.

Now:
- Split pending users into those with and without credentials
- For users without credentials, update nextSyncAt to retry in 24 hours
- Log a warning with affected user IDs
- Only return users with valid credentials for job processing

This prevents log spam and unnecessary database queries while still
periodically checking if credentials have been restored.

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

src/backend/services/auto-sync.service.js

@@ -237,6 +237,7 @@ export async function getPendingSyncUsers(service) {
     const enabledField = service === 'lotw' ? autoSyncSettings.lotwEnabled : autoSyncSettings.dclEnabled;
     const nextSyncField = service === 'lotw' ? autoSyncSettings.lotwNextSyncAt : autoSyncSettings.dclNextSyncAt;
     const credentialField = service === 'lotw' ? users.lotwUsername : users.dclApiKey;
+    const intervalField = service === 'lotw' ? autoSyncSettings.lotwIntervalHours : autoSyncSettings.dclIntervalHours;
 
     const now = new Date();
 
@@ -261,13 +262,45 @@ export async function getPendingSyncUsers(service) {
         )
       );
 
-    // Filter out users without credentials
+    // Split into users with and without credentials
     const withCredentials = results.filter(r => r.hasCredentials);
+    const withoutCredentials = results.filter(r => !r.hasCredentials);
+
+    // For users without credentials, update their next sync time to retry in 24 hours
+    // This prevents them from being continuously retried every minute
+    if (withoutCredentials.length > 0) {
+      const retryDate = new Date();
+      retryDate.setHours(retryDate.getHours() + 24);
+
+      for (const user of withoutCredentials) {
+        const updateData = {
+          updatedAt: new Date(),
+        };
+
+        if (service === 'lotw') {
+          updateData.lotwNextSyncAt = retryDate;
+        } else {
+          updateData.dclNextSyncAt = retryDate;
+        }
+
+        await db
+          .update(autoSyncSettings)
+          .set(updateData)
+          .where(eq(autoSyncSettings.userId, user.userId));
+      }
+
+      logger.warn('Skipped auto-sync for users without credentials, will retry in 24 hours', {
+        service,
+        count: withoutCredentials.length,
+        userIds: withoutCredentials.map(u => u.userId),
+      });
+    }
 
     logger.debug('Found pending sync users', {
       service,
       total: results.length,
       withCredentials: withCredentials.length,
+      withoutCredentials: withoutCredentials.length,
     });
 
     return withCredentials;