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/api-tests/run.ts

@@ -114,6 +114,10 @@ async function setupDatabase() {
     await testSql`INSERT INTO module_config (slug, name, description, licensed, enabled) VALUES (${m.slug}, ${m.name}, ${m.description}, true, ${m.enabled}) ON CONFLICT (slug) DO NOTHING`
   }
 
+  // Seed test email provider so email endpoints work without real provider
+  await testSql`INSERT INTO app_settings (key, value, is_encrypted) VALUES ('email.provider', 'test', false) ON CONFLICT (key) DO NOTHING`
+  await testSql`INSERT INTO app_settings (key, value, is_encrypted) VALUES ('email.from_address', 'Test Store <noreply@test.com>', false) ON CONFLICT (key) DO NOTHING`
+
   await testSql.end()
   console.log('  Database ready')
 }