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/delivery/classes.emailsignjob.ts

@@ -1,5 +1,6 @@
 import * as plugins from '../../plugins.js';
 import type { UnifiedEmailServer } from '../routing/classes.unified.email.server.js';
+import { RustSecurityBridge } from '../../security/classes.rustsecuritybridge.js';
 
 interface Headers {
   [key: string]: string;
@@ -28,24 +29,13 @@ export class EmailSignJob {
 
   public async getSignatureHeader(emailMessage: string): Promise<string> {
     const privateKey = await this.loadPrivateKey();
-    const signResult = await plugins.dkimSign(emailMessage, {
-      signingDomain: this.jobOptions.domain,
+    const bridge = RustSecurityBridge.getInstance();
+    const signResult = await bridge.signDkim({
+      rawMessage: emailMessage,
+      domain: this.jobOptions.domain,
       selector: this.jobOptions.selector,
       privateKey,
-      canonicalization: 'relaxed/relaxed',
-      algorithm: 'rsa-sha256',
-      signTime: new Date(),
-      signatureData: [
-        {
-          signingDomain: this.jobOptions.domain,
-          selector: this.jobOptions.selector,
-          privateKey,
-          algorithm: 'rsa-sha256',
-          canonicalization: 'relaxed/relaxed',
-        },
-      ],
     });
-    const signature = signResult.signatures;
-    return signature;
+    return signResult.header;
   }
 }