Don't offer rooms without posting permission in the forwarding room list

**Is your feature request related to a problem? Please describe.**
(for illustration only. the actual problem is when a room without permission tops the list even without searching.)

**Describe the solution you'd like**
Hide rooms one can't forward to by default.
Show them last when explicitly searching in order to show the "you don't have permission" tooltip.

**Describe alternatives you've considered**
/

**Additional context**
While usually I would want the same ordering as in the Ctrl+K switcher for forwarding, this case diverges from that.

Start by tracing the forwarding room list described in the issue and identify where room ordering, search results, and posting permissions are handled. Confirm the behavior for rooms without forwarding permission: hide them by default, but show them last during an explicit search with the permission tooltip still available.

Written by the indexing model from the issue text.