Migrate all chi imports from github.com/go-chi/chi (v1.5.5) to
github.com/go-chi/chi/v5 (v5.2.1) to resolve GO-2026-4316 open
redirect vulnerability in the RedirectSlashes middleware.
Changes:
- go.mod: replaced chi v1.5.5 with chi/v5 v5.2.1
- Updated import paths in server, routes, middleware, and handlers
- No API changes required (chi/v5 is API-compatible for our usage)
closes #42