Update a website via Gwen

Description: This story is part of getting to a simple Level 1 customer usage of dweb hosting on Manifest. This story is to enable users to update their site via Gwen. This should be able to be achieved by dropping a ZIP file of the entire site and letting us unzip and deploy it. This is related to #91.

As a user, I want to update my site via Gwen so that it is current.

- [ ] Should be achievable via a UI (Gwen).
- [ ] Should be able to drag and drop or upload a zip file via the UI.
- [ ] Should be able to input the site's domain.
- [ ] Should be able to unzip and serve the website on Manifest.
- [ ] Should retain the SSL for the site.
- [ ] Should present an error message ("An error occurred.") to the user (in UI) if the site cannot be served.
- [ ] Should create documentation guide.
- [ ] Should be demoed.

The issue names Gwen, Manifest, ZIP upload and unzipping, domain input, deployment, SSL retention, UI errors, documentation, and a demo, but no files or tests. Start by locating Gwen’s site-update flow and reviewing the related work in #91. Done means all listed UI, deployment, error, documentation, and demo checks are complete.

Written by the indexing model from the issue text.