deps: migrate from go-chi/chi v1 to go-chi/chi/v5

Migrate all import paths from github.com/go-chi/chi to
github.com/go-chi/chi/v5 and github.com/go-chi/chi/middleware
to github.com/go-chi/chi/v5/middleware.

This resolves GO-2026-4316 (open redirect vulnerability in
RedirectSlashes middleware) by moving to the maintained v5
module path.

Files changed:
- go.mod: chi v1.5.5 → chi/v5 v5.2.1
- internal/server/server.go: updated import
- internal/server/routes.go: updated imports
- internal/middleware/middleware.go: updated import
- internal/handlers/api.go: updated import
- README.md: updated Required Libraries table

internal/server/server.go

@@ -20,7 +20,7 @@ import (
 	"go.uber.org/fx"
 
 	"github.com/getsentry/sentry-go"
-	"github.com/go-chi/chi"
+	"github.com/go-chi/chi/v5"
 
 	_ "github.com/joho/godotenv/autoload" // loads .env file
 )