[Story] EX multi-account: switch account

### Description

* As a user with multiple signed-in accounts
* I want to quickly switch between my accounts
* So that I can move between my identities without repeated sign-in

# Acceptance criteria
- Given the user is on the main/room-list screen, when they swipe vertically on their profile avatar, then the app switches to another signed-in account.
- Given the user opens the account list, when there is more than one signed-in account, then the non-active accounts are shown in a collapsible panel, ordered so that the account most recently is at the top, etc.
- Given the user opens the account list, when there is more than one signed-in account, then the notifications count is shown for each of the non-active accounts in case it is greater than 0.
- Given the user expands or collapses the account panel, when they return to it later, then its expanded/collapsed state is remembered.

# Dependencies
- None

# Out of scope
- Nothing

# Questions
- [ ] We did not discuss yet showing the notifications count for the non-active accounts.

# Subtasks

### Android
-

### iOS
-

### Rust
-

### Other
-

Start by reviewing the Android, iOS, and Rust sections of issue #3328; no implementation files or tests are identified. Break the acceptance criteria into platform-specific work, then verify account switching, account ordering, notification counts, and remembered panel state on the main/room-list screen.

Written by the indexing model from the issue text.