feat: add email feature flag, staging bypass, and postinstall

[kevinrutledge]

Developer

Kevin Rutledge

What changed?

Three changes to unblock Vercel staging deployment:

1. EMAIL_ENABLED feature flag - email sending is now gated behind an env var (default: false). SMTP vars are optional when email is disabled. Follows the same pattern as SMS_ENABLED. Includes EMAIL_REDIRECT_TO for safe testing - when set, all emails go to that address instead of real recipients.

2. STAGING env var - mock portal and dev token route now allow access when STAGING=true, even on production NODE_ENV. This lets the staging site use the mock portal for login since there is no real Member Portal integration.

3. postinstall script - adds prisma generate to postinstall so Vercel regenerates the Prisma Client when restoring cached node_modules.

Also fixes deprecated React.FormEvent type in mock portal.

How to test

1. Run npm test - 237 tests pass
2. Run npm run build - succeeds
3. Start dev server without SMTP vars, with EMAIL_ENABLED=false - app loads, referral form creates records without sending email
4. Start dev server with EMAIL_ENABLED=true and EMAIL_REDIRECT_TO=your@email.com - emails redirect to that address with original recipient in subject line
5. Set STAGING=true - /dev/mock-portal accessible regardless of NODE_ENV

Checklist

• Code works and is readable
• Tested locally
• Commits follow conventional commits
• Assigned reviewers