deps: migrate from chi v1 to chi/v5

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

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
 )