Add post-installation redirect based on admin account status (#34493)

This PR adds a feature to direct users to appropriate pages after system
installation:
- If no admin credentials were provided during installation, redirect to
the registration page with a prominent notice about creating the first
administrative account
- If admin credentials were already set, redirect directly to the login
page


![4d396ad132d9b57fc4f45a62117177f1](https://github.com/user-attachments/assets/3a5d8700-9194-4d3b-a862-e64c8c347932)

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

routers/install/install.go

@@ -601,5 +601,7 @@ func SubmitInstall(ctx *context.Context) {
 // InstallDone shows the "post-install" page, makes it easier to develop the page.
 // The name is not called as "PostInstall" to avoid misinterpretation as a handler for "POST /install"
 func InstallDone(ctx *context.Context) { //nolint
+	hasUsers, _ := user_model.HasUsers(ctx)
+	ctx.Data["IsAccountCreated"] = hasUsers.HasAnyUser
 	ctx.HTML(http.StatusOK, tplPostInstall)
 }