Allow uploading custom HTML for pages

Add the ability to upload the customer's own HTML to pages instead of having to use AI to create them. Editing a page with AI is described as very slow and laborious: it can produce a good working starting place, but the actual editing takes hours compared to a wysiwyg editor or just prompting HTML changes. Wysiwyg editors exist that can output HTML, and AI tools can output HTML and apply requested edits quickly. Uploading HTML would also bring more functionality, including things like cookie management, which is not currently possible.