fix(email): type the metadata slot lookup so the ratchet holds (#4509)

CI's slot-lookup ratchet caught the bridge's `ctx.getService('metadata')`:
email-plugin.ts is grandfathered for its three existing erasures, and a new
untyped lookup pushed it to four. Pass the slot's contract type
(`IMetadataService`) as #4251 asks — which also gives the subscribe/get calls a
real type instead of `any`.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01E5CYr5SDwe85gH2Jr5KSgu

Author: claude

packages/plugins/plugin-email/src/email-plugin.ts

@@ -5,6 +5,7 @@ import type { IDataEngine } from '@objectstack/spec/contracts';
 import type {
   IEmailTransport,
   EmailAddress,
+  IMetadataService,
 } from '@objectstack/spec/contracts';
 import { SysEmail, SysEmailTemplate } from '@objectstack/platform-objects/audit';
 import { EmailService, LogTransport, type EmailPersistence, type TemplateLoader, type EmailTemplateRow } from './email-service.js';
@@ -415,8 +416,8 @@ export class EmailServicePlugin implements Plugin {
       ctx.logger.warn('EmailServicePlugin: template provenance stamp not bound: ' + (err?.message ?? err));
     }
 
-    let metadataService: any;
-    try { metadataService = ctx.getService('metadata'); } catch { /* optional */ }
+    let metadataService: IMetadataService | undefined;
+    try { metadataService = ctx.getService<IMetadataService>('metadata'); } catch { /* optional */ }
 
     try {
       await bootstrapDeclaredEmailTemplates(engine, metadataService, ctx.logger as any);