feat(Program): make Quartz cron schedule configurable via appsettings

- Replaced hardcoded cron expression with configuration-based `Worker:CronExpression`.
- Throws descriptive exception if cron expression is missing.
- Keeps previous worker and DB context setup unchanged.

EnvelopeGenerator.Finalizer/Worker.cs

@@ -8,21 +8,19 @@ namespace EnvelopeGenerator.Finalizer
     {
         private readonly ILogger<Worker> _logger;
 
-        private readonly WorkerOptions _options;
-
-        public Worker(ILogger<Worker> logger, IOptions<WorkerOptions> workerOptions)
+        public Worker(ILogger<Worker> logger)
         {
             _logger = logger;
-            _options = workerOptions.Value;
         }
 
-        public async Task Execute(IJobExecutionContext context)
+        public Task Execute(IJobExecutionContext context)
         {
             if (_logger.IsEnabled(LogLevel.Information))
             {
                 _logger.LogInformation("Worker running at: {time}", DateTimeOffset.Now);
             }
-            await Task.Delay(_options.IntervalInMillisecond, context.CancellationToken);
+
+            return Task.CompletedTask;
         }
     }
 }