feat: implement comprehensive route-based email routing system

Replace legacy domain-rule based routing with flexible route-based system that supports:
- Multi-criteria matching (recipients, senders, IPs, authentication)
- Four action types (forward, process, deliver, reject)
- Moved DKIM signing to delivery phase for signature validity
- Connection pooling for efficient email forwarding
- Pattern caching for improved performance

This provides more granular control over email routing with priority-based matching and comprehensive test coverage.

ts/mail/index.ts

@@ -1,7 +1,6 @@
 // Export all mail modules for simplified imports
 export * from './routing/index.js';
 export * from './security/index.js';
-export * from './services/index.js';
 
 // Make the core and delivery modules accessible
 import * as Core from './core/index.js';