Mapping external API calls through Express backend

[elainefan331]

Description:
The frontend currently makes direct browser requests to https://neurojson.io:7777 to fetch data. Port 7777 is a non-standard port and is commonly blocked by school and corporate firewalls, which only allow outbound traffic on ports 80 and 443. This causes data to silently fail and show as -- for affected users.
All external API calls should be mapped through the Express backend.

Tasks:

• Update frontend neurojson service to call Express routes instead of external URLs directly
• Add routes in backend for all CouchDB and neurojson.org endpoints

Acceptance criteria:

• No browser request to :7777 is visible in the network tab — all traffic goes through express backend
• All data loads correctly with no silent failures