[Story] EX multi-account: reorganize settings for multi-account (app-level vs. account-level)

### Description

* As a user with multiple signed-in accounts
* I want to find app-wide settings kept separate from account-specific settings
* So that I understand which settings apply to all my accounts and which apply only to the currently active one

# Acceptance criteria
- Given the user opens Settings, when they look for
- Appearance,
- View source (to be moved to Developer Settings),
- Optimise image upload quality,
- Video upload quality,
- Screen lock/PIN,
- About,
- Developer tools,
- Live location updates,
- Labs,
- and Analytics, then these appear under an "App settings" area rather than nested per account.
- Given the user opens Settings, when they look for "Report a problem", then it remains under the account-specific area.
- Given the user clears cache from Developer Settings, then cache for all signed-in accounts is cleared, not just the active one.
- Given the user has previously opted in/out of Analytics, when they sign in to additional accounts, then that decision is remembered at the app level rather than reset, for as long as at least one account is signed in.
- Given the user signs out from all of their accounts, when they sign in to first account again, then they are asked again to opt in/out to Analytics.

# Dependencies
- None

# Out of scope
- Clearing the cache could be technically done per account, however this is better suited to be done when making this function available to non-developers (e.g. moved out from Developer Settings). We don't want to increase the multi-account scope with that
- While users may need different video/image quality for different accounts, this is better to be addressed by allow the user to adjust the quality (e.g. the default in the settings) for a particular upload since this is more flexible. However, this is out of the scope of this project

# Questions
- [ ] There's still uncertainty about which visual design is the best. Should we keep both type of setting in one flat list (separated into 2 blocks), or should the account settings be extracted into a sub menu which you can see when pressing the arrow on your active account. @americanrefugee is exploring this topic further.

# Subtasks

### Android
-

### iOS
-

### Rust
-

### Other
-

The issue names no files, tests, or implementation entry points. Start by resolving the open visual-design question and splitting the story into Android, iOS, and Rust subtasks. Done means the listed settings are separated by scope, cache clearing is app-wide, and Analytics consent follows the stated sign-in and sign-out rules.

Written by the indexing model from the issue text.