Implement Workstream G: Email Service with Postmark

- Add postmark dependency and email configuration constants
- Implement sendVerificationEmail, sendPasswordResetEmail,
  sendLoginConfirmationEmail, and sendOrgInviteEmail helpers
- Add HTML + text email templates with inline CSS
- Support dev mode (EMAIL_DEV_MODE=true) for console logging
- Use URL constructor for proper URL building
- Add XSS protection with HTML escaping in templates
- Create .env file with email environment variables

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/api-server/package.json

@@ -18,6 +18,7 @@
     "@simplewebauthn/server": "^13.2.2",
     "@simplewebauthn/types": "^12.0.0",
     "kysely": "^0.28.2",
+    "postmark": "^4.0.5",
     "zxcvbn": "^4.4.2"
   },
   "devDependencies": {