Improve error logging and add user guidance for issue reporting

- Added fatal log in `login.go` for Cloud AI API enablement check failures, prompting users to report issues.
- Enhanced error logging in `client.go` with warning messages directing users to copy and provide error details when creating issues.

internal/auth/auth.go

@@ -168,11 +168,12 @@ func getTokenFromWeb(ctx context.Context, config *oauth2.Config) (*oauth2.Token,
 	codeChan := make(chan string)
 	errChan := make(chan error)
 
-	// Create a new HTTP server.
-	server := &http.Server{Addr: ":8085"}
+	// Create a new HTTP server with its own multiplexer.
+	mux := http.NewServeMux()
+	server := &http.Server{Addr: ":8085", Handler: mux}
 	config.RedirectURL = "http://localhost:8085/oauth2callback"
 
-	http.HandleFunc("/oauth2callback", func(w http.ResponseWriter, r *http.Request) {
+	mux.HandleFunc("/oauth2callback", func(w http.ResponseWriter, r *http.Request) {
 		if err := r.URL.Query().Get("error"); err != "" {
 			_, _ = fmt.Fprintf(w, "Authentication failed: %s", err)
 			errChan <- fmt.Errorf("authentication failed via callback: %s", err)

internal/client/client.go

@@ -771,6 +771,7 @@ func (c *Client) CheckCloudAPIIsEnabled() (bool, error) {
 					)
 				}
 			}
+			log.Warnf("\n\nPlease copy this message and create an issue.\n\n%s\n\n", errJson)
 			return false, nil
 		}
 		return false, err.Error

internal/cmd/login.go

@@ -73,6 +73,7 @@ func DoLogin(cfg *config.Config, projectID string) {
 		// If the check fails (returns false), the CheckCloudAPIIsEnabled function
 		// will have already printed instructions, so we can just exit.
 		if !isChecked {
+			log.Fatal("Failed to check if Cloud AI API is enabled. If you encounter an error message, please create an issue.")
 			return
 		}
 	}