Add /devices/register/ route alias for mobile clients

The KMM mobile app calls /api/notifications/devices/register/ but
the Go API had /api/notifications/devices/. Added alias to support both.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

docs/DOKKU_SETUP.md

@@ -220,7 +220,7 @@ dokku config:set casera-api \
   EMAIL_USE_TLS=true \
   EMAIL_HOST_USER=treytartt@fastmail.com \
   EMAIL_HOST_PASSWORD=2t9y4n4t497z5863 \
-  DEFAULT_FROM_EMAIL="Casera <noreply@casera.com>"
+  DEFAULT_FROM_EMAIL="Casera <treytartt@fastmail.com>"
 ```
 
 ### 3. Apple Sign In (Optional)