remove dead Auth() middleware method

The Auth() method in internal/middleware/middleware.go only logged and
passed through without performing any actual authentication. It was
never referenced anywhere in the codebase — authentication is handled
per-handler via requireAuth in the handlers package.

closes #38

internal/middleware/middleware.go

@@ -142,20 +142,6 @@ func (mware *Middleware) CORS() func(http.Handler) http.Handler {
 	})
 }
 
-// Auth returns middleware that performs authentication.
-func (mware *Middleware) Auth() func(http.Handler) http.Handler {
-	return func(next http.Handler) http.Handler {
-		return http.HandlerFunc(
-			func(
-				writer http.ResponseWriter,
-				request *http.Request,
-			) {
-				mware.log.Info("AUTH: before request")
-				next.ServeHTTP(writer, request)
-			})
-	}
-}
-
 // Metrics returns middleware that records HTTP metrics.
 func (mware *Middleware) Metrics() func(http.Handler) http.Handler {
 	metricsMiddleware := ghmm.New(ghmm.Config{ //nolint:exhaustruct // optional fields