iOS keychain persistence

### What is this about?

Sentry logging is showing an increase in iOS keychain persistence issues. Where the users password and other metadata seem to be wiped from the keychain. Below is a common stack trace and error flow for these iOS users.

```
Error: Login/ handleVaultCorruption: getVaultFromBackup failed to retrieve vault
at ?anon_0_ (app/components/Views/Login/index.tsx:321:24)
at next (native)
at asyncGeneratorStep (node_modules/@babel/runtime/helpers/asyncToGenerator.js:3:17)
at _next (node_modules/@babel/runtime/helpers/asyncToGenerator.js:17:27)
at tryCallOne (app:///main.jsbundle:1:1181)
at anonymous (app:///main.jsbundle:1:1875)
```

### Scenario

_No response_

### Design

_No response_

### Technical Details

_No response_

### Threat Modeling Framework

_No response_

### Acceptance Criteria

_No response_

### Stakeholder review needed before the work gets merged

- [ ] Engineering (needed in most cases)
- [ ] Design
- [ ] Product
- [ ] QA (automation tests are required to pass before merging PRs but not all changes are covered by automation tests - please review if QA is needed beyond automation tests)
- [ ] Security
- [ ] Legal
- [ ] Marketing
- [ ] Management (please specify)
- [ ] Other (please specify)

### References

_No response_

Start with app/components/Views/Login/index.tsx around line 321, where the reported stack trace shows handleVaultCorruption calling getVaultFromBackup. Trace the iOS keychain persistence and backup flow, then reproduce the reported vault-loss scenario. Done should demonstrate that the affected password and metadata remain recoverable and that the failure path is covered by verification.

Written by the indexing model from the issue text.