Problem

Next.js Server Components require absolute URLs to fetch data (http://...),
while client-side code needs relative URLs to avoid CORS issues in
containerized deployments.

Currently, the code uses a single URL that breaks when deployed in containers
or multi-host setups.

Solution

Formalize a pattern for Client vs Server API URLs with:

1. Different environment variables for each context
2. Helper utilities to get the correct URL based on context
3. Documentation on how to configure for different deployment scenarios

Example

• Client: NEXT_PUBLIC_LEARNHOUSE_API_URL=/api/v1/
• Server: LEARNHOUSE_API_URL_INTERNAL=http://backend:8000/api/v1/

Impact

Makes containerized deployments easier, supports multi-host setups,
improves developer experience.

See: #515 (Your PR reference)