feat: runtime-configurable API URL via Next.js API route proxy

[wrigjl]

Closes #99

Summary

• Replaces NEXT_PUBLIC_REDUX_BASE_URL (baked into the JS bundle at build time) with a server-side REDUX_BASE_URL read at request time by a Next.js API route proxy at /api/redux/[...path]
• The frontend hardcodes /api/redux/ as its base URL; the proxy forwards all requests to the real API, preserving method, headers, query string, and body
• Returns clear JSON errors on misconfiguration (REDUX_BASE_URL not set → HTTP 500) or upstream failure (unreachable → HTTP 502)
• One Docker image works for every environment — set the API URL at docker run time:

  docker run -e REDUX_BASE_URL=https://api.redux.portneuf.cose.isu.edu/ ...
  

Key files

File	Change
pages/api/redux/[...path].js	New proxy route
pages/index.js	Base URL → /api/redux/
.env.development	Renamed var to REDUX_BASE_URL (value unchanged)
.env.production	Removed REDUX_BASE_URL (no default baked into image)
next.config.js	Reverted — rewrites are evaluated at build time, not runtime
Dockerfile	Removed stale NEXT_PUBLIC_REDUX_BASE_URL build arg

Test plan

• Built Docker image without REDUX_BASE_URL set; hitting /api/redux/* returns {"error":"REDUX_BASE_URL is not configured"}
• Ran container with -e REDUX_BASE_URL=http://redux.thought.net:27000/; real API responded correctly through the proxy
• npm run dev still uses localhost:27000 via .env.development

Note on rewrites

The issue proposed using next.config.js rewrites. Investigation showed that the rewrite destination is resolved at next build time and compiled into server.js — runtime env vars have no effect. An API route is the correct approach for true runtime configurability.

🤖 Generated with Claude Code

[Trosper3]

Surprising to me still that the old environment variable was baked at build time. I think this will help make our Docker images more flexible.