Controlled forms and inputs should always have a `value`

When using the controlled options

  form_props(controlled: true, model: Post.new) do |f|
    f.text :title
  end

The output does not contain a value

      "inputs": {
        "title": {
          "type": "text",
          "name": "post[title]",
          "id": "post_title"
        },

This poses a problem in react land because if there suddenly is a value, react will say something to the effect of "uncontrolled component suddenly becomes controlled". So if controlled is used anywhere, we should give it a default value of nil or maybe empty "". I'm not sure which one makes the most sense, and would love some opinions.

Start by tracing the controlled form_props example and the f.text path that produces the shown input JSON. Check existing form helper tests or output fixtures for controlled fields, then determine the project's expected default value behavior. Done means controlled inputs consistently include a value without breaking existing output or React integration.