End user cannot configure widgets

### Steps to reproduce

The end user is unable to configure widgets by using Element, except in a limited capacity by using /devtools, /addwidget, or using the integration manager. The integration manager is only usable for a small number of 1p widgets, and the other methods are too difficult for a normal user. Addwidget does not allow changing the name or icon of the widget, and only works for rooms, not for account scoped widgets.

This means that it's impossible for a widget developer to ship a widget to end users who are using Element. As a result, widget development is effectively futile, so long as most users use Element.

### Outcome

Widget developers should have a way to ship widgets that end users can install in rooms and their account.

### Operating system

_No response_

### Browser information

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### URL for webapp

_No response_

### Application version

_No response_

### Homeserver

_No response_

### Will you send logs?

Yes

Start by reviewing the existing /devtools and /addwidget flows and the integration manager described in the issue. Determine how room-scoped and account-scoped widgets are handled, then define a user-facing installation flow that supports widget names and icons and works for both scopes.

Written by the indexing model from the issue text.