"Export as HTML" could just emit a webpage rather than a fancy ZIP, for better UX

### Steps to reproduce

1. Export a room as HTML
2. Get a zip file, with bits of HTML and CSS and attachments etc in it.
3. Watch as less technical users get confused with wrangling a ZIP file, and opening stuff at random until they find messages.html

### Outcome

#### What did you expect?

Just open a webpage with the static exported history on it. This has the advantage that:
* You can immediately preview what got exported
* You can save it however your browser likes (e.g. "save as web file, complete" in Chrome)
* You can print to PDF if you so desire.
* You use the existing UI/UX for manipulating HTML archives, rather than inventing an entirely new thing which is neither MHTML nor MAFF nor Web Archive or whatever.

#### What happened instead?

The app assumed the user was a developer who would know how to handle a ZIP of HTML+CSS, rather than treating them like a normal user.

### Operating system

_No response_

### Browser information

_No response_

### URL for webapp

_No response_

### Application version

_No response_

### Homeserver

_No response_

### Will you send logs?

No