Feature request: Overwrite mode

I would love to have a "Dev mode / Overwrite mode" that would never write any templates to the database, but always save them directly to the theme files instead.

I tested the Gutenberg patch that got dropped in favor of this, and I actually somewhat liked it better to be able to save templates from the editor itself. Not exactly like it was done, I rather just have one button to save all templates. Or, even better, what I suggested above.

As I am developping my first FSE theme, the only option that makes sense to me is to overwrite. And it's an additional hassle to have another tab open and having to manually save the template changes. The menu is very out-of-place IMO, it would be more fitting to have it directly inside the Site Editor, or at least the override option.

Start by reviewing the plugin's current template-saving flow and its Site Editor integration, then compare the dropped Gutenberg patch mentioned in the issue. Before implementation, clarify whether the goal is a development mode, a single save-all action, or an override option; done should mean template changes bypass the database and are saved to theme files.