fix: add gzip/brotli response compression middleware (#128)

[LaGodxy]

Summary

Adds compression middleware to the NestJS bootstrap function, enabling gzip and brotli encoding for API responses. Large JSON payloads (campaign lists, claim exports) are now compressed automatically, reducing bandwidth usage and improving response times on slow connections.

Changes

• Install compression npm package
• Add app.use(compression()) in main.ts after security middleware

Testing

Build passes. Compression is transparent to clients that send Accept-Encoding: gzip or br.

Closes #128

[kilodesodiq-arch]

LGTM