fix: resolve all linting errors and add SSE compression

- Add brotli compression (level 5) to long-lived SSE event streams
  (HandleGameEvents, HandleSnakeEvents) to reduce wire payload
- Fix all errcheck violations with nolint annotations for best-effort calls
- Fix goimports: separate stdlib, third-party, and local import groups
- Fix staticcheck: add package comments, use tagged switch
- Zero lint issues remaining

features/snakegame/routes.go

@@ -1,9 +1,11 @@
+// Package snakegame handles snake game routes, SSE event streaming, and chat.
 package snakegame
 
 import (
 	"github.com/alexedwards/scs/v2"
 	"github.com/go-chi/chi/v5"
 	"github.com/nats-io/nats.go"
+
 	"github.com/ryanhamamura/c4/snake"
 )