Fix critical race conditions and performance issues

- Implement atomic check-and-create pattern in ensureEmailJob with exponential backoff
- Fix import mismatch by exporting processJobById from index.ts
- Enable database indexes for status+scheduledAt and priority+createdAt fields
- Standardize string conversion for consistent ID handling throughout codebase
- Fix TypeScript compilation errors in collection indexes and variable scope

🤖 Generated with [Claude Code](https://claude.ai/code)

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

src/index.ts

@@ -29,7 +29,7 @@ export {
 } from './utils/helpers.js'
 
 // Email processing utilities
-export { processEmailById, processAllEmails } from './utils/emailProcessor.js'
+export { processEmailById, processJobById, processAllEmails } from './utils/emailProcessor.js'
 
 // Job scheduling utilities
 export { findExistingJobs, ensureEmailJob, updateEmailJobRelationship } from './utils/jobScheduler.js'