feat: warn users when `personal_sign` message contains the string "wants you to sign in with your Ethereum account"

### What is this about?

Complete the following requirement of https://github.com/MetaMask/MetaMask-planning/issues/2278:
[ ] Ensure we warn the user when a personal_sign message contains the string "wants you to sign in with your Ethereum account". (see first recommendation here: https://eips.ethereum.org/EIPS/eip-4361#wallet-implementer-steps)

### Scenario

_No response_

### Design

We can use a warning banner alert for this. Copy and details should be discussed with design

### 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_

No file, test, or entry point is named. Locate the personal_sign handling and existing warning-banner components, then review the EIP-4361 wallet implementer steps and the design discussion. Done means the specified message string triggers a user warning with agreed copy and appropriate automated coverage.

Written by the indexing model from the issue text.