Backend & admin panel for existing AI chatbot

I have a fully working AI guest assistant chatbot (single HTML/JS file, built and tested). I need a full stack developer to build the backend around it.
THE FRONTEND IS DONE — this is purely a backend job.
What I need:

Secure API proxy — move the Anthropic Claude API call server-side, API key stored in environment variables
Database (PostgreSQL or Firebase) — store property records with name, guide text, video links
Admin panel (password protected) — add/edit/delete properties, auto-generate unique guest URL per property
Dynamic guest page — chatbot loads correct property guide based on URL e.g. mysite.co.uk/guest/naia
Hosting & deployment — subdomain on my existing hosting, must handle 20-50 properties

I will provide: the working HTML file, Anthropic API key, hosting access.
Please only apply if you have built secure backend systems before and can share a relevant example.