ritampaine75-debug/OTP-verification-free- ? reverse-engineered prompt

Build me a full email OTP verification app that uses Gmail to send the codes and Firebase Realtime Database to store the verification state. I want a simple flow where a user enters their email, gets a 6 digit code, then confirms it in the app, with the code expiring after a few minutes and getting deleted once it is used.

Please make it feel production ready, with basic security like storing only a hashed version of the code, limiting wrong attempts, and preventing spam requests if someone keeps asking for new codes too fast. I also want a small diagnostics page or check route so I can see if the backend, email sending, and database connection are working.

Use the existing setup in the repo and make it work end to end, and if you need to look up current docs online for anything, do that.