Fix build tag and pass gosec security checks

Author: Saharyasa

keepalive_staticcheck.go

@@ -1,28 +1,11 @@
-package main
-
-// References otherwise-unused symbols so staticcheck (U1000) doesn't fail in the tutorial repo.
-// No runtime effect.
+//go:build staticcheck
+// +build staticcheck
 
-var (
-	// Methods on *apiConfig — use method expressions
-	_ = (*apiConfig).handlerNotesGet
-	_ = (*apiConfig).handlerNotesCreate
-	_ = (*apiConfig).handlerUsersCreate
-	_ = (*apiConfig).handlerUsersGet
-	_ = (*apiConfig).middlewareAuth
+package main
 
-	// Plain functions
-	_ = handleReadiness
-	_ = generateRandomSHA256Hash
-	_ = respondWithError
-	_ = respondWithJSON
-	_ = writeJSON
+import "net/http"
 
-	// Types / zero values
-	_ = authMiddleware{}
+// Stubs only for the staticcheck build tag.
+func handleReadiness(w http.ResponseWriter, r *http.Request) {}
 
-	// Model mapping helpers
-	_ = databaseUserToUser
-	_ = databaseNoteToNote
-	_ = databasePostsToPosts
-)
+func authMiddleware(next http.Handler) http.Handler { return next }