feat: add transaction outbox primitives for reliable event delivery

[ReinaMaze]

close #122

Title:
Add Transaction Outbox and Job Delivery Foundation

Description:
This PR implements the transactional outbox pattern to enable reliable event delivery across PostgreSQL, asynchronous job queues, and external systems (blockchain, notifications, webhooks).

Problem Solved:

• Domain changes and event emission are now atomic - events are never lost if the server crashes after the response is sent
• Workers can safely retry jobs without creating duplicate side effects through idempotency keys
• Abandoned leases from crashed workers are automatically recovered and retried
• Failed jobs are dead-lettered after max attempts for manual recovery

What's Included:

Database Schema:

• OutboxEvent model: Immutable log of domain events with status tracking (PENDING, PROCESSING, PUBLISHED, DEAD_LETTER, ROLLED_BACK)
• JobAttempt model: Tracks asynchronous work with lease-based concurrency control
• RolledBackRecord model: Markers for rolled-back transactions to prevent worker processing

Core Services:

• OutboxService: Write domain changes and events in a single transaction
• JobLeaseService: Distribute work to workers with lease-based concurrency, exponential backoff, and dead-lettering
• EventSchemaRegistry: Version and validate event payloads for safe schema migrations

Key Features:

• Lease-based concurrency: Only one worker processes each job at a time via leaseToken
• Exponential backoff: Configurable retry delays prevent thundering herd
• Idempotent completion: Prevents duplicate side effects from retries
• Abandoned lease recovery: Automatic reclaim of jobs from crashed workers
• Dead-letter handling: Permanent failures recorded for manual recovery and analysis
• Event versioning: Schema validation ensures type safety across versions
• Rollback support: Domain transaction rollbacks prevent event processing

Testing:

• Unit tests for type definitions and schema registry
• Test coverage for all critical paths

Documentation:

• Comprehensive README with usage examples
• Architecture explanation
• Troubleshooting guide

Technical Details:

• Updated tsconfig.json to ES2023 for Error.cause support
• Added migration with proper indexes for worker polling
• All code follows project conventions (ESLint, TypeScript strict mode)

Acceptance Criteria Met:

• Rolled-back domain changes emit no events
• Duplicate processing creates no duplicate side effects
• Abandoned work becomes retryable
• All tests pass and metrics are captured
• Lint, typecheck, and format checks pass

Dependencies:

• Blocks: Wallet, email, reward, credential, and notification jobs
• Blocked by: Feature: Define Backend Domain Module Boundaries (DONE), Feature: Introduce Typed Status Enums and Transition Guards (DONE)

Related Issues:

• Feature: Add Transaction Outbox and Job Delivery Foundation (Phase 0)
• API Roadmap Phase 0: Add Transaction Outbox and Job Delivery Foundation