feat(auth): confirm the e-mail address of new accounts by link

- Setting / REGISTRATION_VERIFY_EMAIL; only with SMTP and BASE_URL; invites skip it
- Hashed one-time tokens (48 h), resend with cooldown, unconfirmed accounts purged
- Approval modes notify admins only after the address is confirmed

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

frontend/package.json

@@ -1,7 +1,7 @@
 {
   "name": "mindsift-frontend",
   "private": true,
-  "version": "0.23.0",
+  "version": "0.24.0",
   "license": "Unlicense",
   "type": "module",
   "scripts": {