[Story] Fix backup decryption key without recovery

### Description

If the (message keys) backup decryption key is missing or not working, we're currently only fixing it when the user has set up recovery. However, since this backup is independent of recovery, we should fix it even when the user is not using recovery. In particular, as we can now do it automatically by creating a new backup and pushing the new key to other devices, without needing recovery to be set up.

# Acceptance criteria
- TBD

# Dependencies
- None

# Out of scope
- Nothing

# Questions
- [x] None

# Subtasks

### Android
-

### iOS
-

### Rust
-

### Web
-

No files, tests, or concrete entry points are named. Review the existing recovery-dependent backup decryption-key repair flow across the Android, iOS, Rust, and Web client areas, then clarify acceptance criteria for creating a new backup and pushing its key to other devices without recovery.

Written by the indexing model from the issue text.