Visiting a private room has UI provide a knock button or "Call not found"

### Steps to reproduce

1. Create a guest link for a knock/public room
2. Change the room access to private
3. Visit the guest link in a new tab

### Outcome

#### What did you expect?
The guest link's ECall should report the room as being private.

#### What happened instead?
One of the two outcomes:

1) The guest link's ECall offers to send a knock to the room, which unsurprisingly fails & shows the server error of:
> MatrixError: [403] You don't have permission to knock (https://matrix.guest.ess-ecall-poc.ems-support.element.dev/_matrix/client/v3/knock/!xDTBDZXIBfULuWWyMZ%3Aess-ecall-poc.ems-support.element.dev?server_name=ess-ecall-poc.ems-support.element.dev)

2) The guest link's ECall reports the call as not found, and displays a message of:
> Call not found
>
> Calls are now end-to-end encrypted and need to be created from the home page. This helps make sure everyone's using the same encryption key.

### Operating system

_No response_

### Browser information

_No response_

### URL for webapp

https://call.guest.ess-ecall-poc.ems-support.element.dev/

### Will you send logs?

No

Start by reproducing the guest-link flow at the webapp URL: create a knock/public room, switch it to private, and open the link in a new tab. Trace the guest-link room lookup and its knock or “Call not found” outcomes; done means a private room is handled consistently without offering a failing knock or misleading not-found state.

Written by the indexing model from the issue text.