feat: email receipts and repair estimates

Backend:
- Server-side HTML email templates (receipt + estimate) with inline CSS
- POST /v1/transactions/:id/email-receipt with per-transaction rate limiting
- POST /v1/repair-tickets/:id/email-estimate with per-ticket rate limiting
- customerEmail field added to receipt and ticket detail responses
- Test email provider for API tests (logs instead of sending)

Frontend:
- POS payment dialog Email button enabled with inline email input
- Pre-fills customer email from linked account
- Repair ticket detail page has Email Estimate button with dialog
- Pre-fills from account email

Tests:
- 12 unit tests for email template renderers
- 8 API tests for email receipt/estimate endpoints and validation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/backend/src/services/email.service.ts

@@ -87,6 +87,21 @@ class SmtpProvider implements EmailProvider {
   }
 }
 
+class TestProvider implements EmailProvider {
+  static lastEmail: SendOpts | null = null
+  static emails: SendOpts[] = []
+
+  async send(opts: SendOpts): Promise<void> {
+    TestProvider.lastEmail = opts
+    TestProvider.emails.push(opts)
+  }
+
+  static reset() {
+    TestProvider.lastEmail = null
+    TestProvider.emails = []
+  }
+}
+
 export const EmailService = {
   async send(db: PostgresJsDatabase<any>, opts: SendOpts): Promise<void> {
     const provider = await SettingsService.get(db, 'email.provider')
@@ -99,8 +114,14 @@ export const EmailService = {
         return new SendGridProvider(db).send(opts)
       case 'smtp':
         return new SmtpProvider().send(opts)
+      case 'test':
+        return new TestProvider().send(opts)
       default:
         throw new Error('Email provider not configured. Set email.provider in app_settings.')
     }
   },
+
+  getTestEmails: () => TestProvider.emails,
+  getLastTestEmail: () => TestProvider.lastEmail,
+  resetTestEmails: () => TestProvider.reset(),
 }