BREAKING CHANGE(rust-bridge): make Rust the primary security backend, remove all TS fallbacks

Phase 3 of the Rust migration: the Rust security bridge is now mandatory
and all TypeScript security fallback implementations have been removed.

- UnifiedEmailServer.start() throws if Rust bridge fails to start
- SpfVerifier gutted to thin wrapper (parseSpfRecord stays in TS)
- DKIMVerifier gutted to thin wrapper delegating to bridge.verifyDkim()
- IPReputationChecker delegates to bridge.checkIpReputation(), keeps LRU cache
- DmarcVerifier keeps alignment logic (works with pre-computed results)
- DKIM signing via bridge.signDkim() in all 4 locations
- Removed mailauth and ip packages from plugins.ts (~1,200 lines deleted)

ts/mail/security/classes.dmarcverifier.ts

@@ -1,9 +1,6 @@
-import * as plugins from '../../plugins.js';
 import { logger } from '../../logger.js';
 import { SecurityLogger, SecurityLogLevel, SecurityEventType } from '../../security/index.js';
-// MtaService reference removed
 import type { Email } from '../core/classes.email.js';
-import type { IDnsVerificationResult } from '../routing/classes.dnsmanager.js';
 
 /**
  * DMARC policy types