refactor: streamline routes to RESTful naming conventions

Remove /api/ prefix and consolidate route groups:
- /api/lobby/* -> /games, /snake, /logout (top-level)
- /game/{game_id} + /api/game/{game_id}/* -> /games/{id}/*
- /snake/{game_id} + /api/snake/{game_id}/* -> /snake/{id}/*
- /api/auth/* -> /auth/*
- Standardize snake join page to use return_url= (was return=)

features/auth/routes.go

@@ -11,8 +11,8 @@ import (
 func SetupRoutes(router chi.Router, queries *repository.Queries, sessions *scs.SessionManager) error {
 	router.Get("/login", HandleLoginPage())
 	router.Get("/register", HandleRegisterPage())
-	router.Post("/api/auth/login", HandleLogin(queries, sessions))
-	router.Post("/api/auth/register", HandleRegister(queries, sessions))
+	router.Post("/auth/login", HandleLogin(queries, sessions))
+	router.Post("/auth/register", HandleRegister(queries, sessions))
 
 	return nil
 }