Fix critical error handling and race condition issues

🔴 Critical fixes:
- Fix race condition: processImmediately now properly fails if job creation fails
- Fix silent job failures: job creation failures now throw errors instead of warnings
- Ensure atomic operations: either email + job succeed together, or both fail

⚠️ Improvements:
- Simplify error handling in processEmailJob to be more consistent
- Add proper validation for missing PayloadCMS jobs configuration
- Make error messages more descriptive and actionable

src/jobs/processEmailJob.ts

@@ -64,13 +64,7 @@ export const processEmailJob = {
         }
       }
     } catch (error) {
-      // Re-throw Error instances to preserve stack trace and error context
-      if (error instanceof Error) {
-        throw error
-      } else {
-        // Only wrap non-Error values
-        throw new Error(`Failed to process email ${emailId}: ${String(error)}`)
-      }
+      throw new Error(`Failed to process email ${emailId}: ${error instanceof Error ? error.message : String(error)}`)
     }
   }
 }