Count errors and skip shelf on token decrypt fail

When decrypting a user's API token fails, increment stats.errors and continue to the next shelf instead of proceeding. This ensures failed decryptions are tracked in metrics and prevents attempting to fetch data with an invalid token.

src/lib/services/hardcover-sync.service.ts

@@ -70,6 +70,8 @@ export async function processHardcoverShelves(
         }
       } catch (err) {
         log.error(`Failed to decrypt API token for user ${shelf.user.plexUsername}`);
+        stats.errors++;
+        continue;
       }
 
       let fetchedData: { listName: string; books: HardcoverApiBook[] };