Add built-in "Wrong Network" guard and switch prompt for Base networks

Acceptance criteria:
- Wrong-network state can be detected without custom app logic.
- Works correctly for Base and Base Sepolia.
- Provides clear UX when network switching is supported and when it is not.
- Includes at least one test covering detection and switch request behavior.

Steps to reproduce:
1. Create an app using OnchainKit wallet components.
2. Configure the app to target Base or Base Sepolia.
3. Connect a wallet while the wallet is set to a different network (e.g., Ethereum mainnet).
4. Observe that wrong-network handling must be implemented manually by the app.

Description:
Many apps built with OnchainKit need to handle the "wrong network" scenario when a user connects a wallet on an unsupported chain. Currently, developers must implement this logic themselves, leading to duplicated code and inconsistent UX across apps in the Base ecosystem.

Providing a built-in solution would improve developer experience and encourage consistent network handling patterns.

Proposed solution:
- Expose a hook (e.g. `useNetworkGuard`) that detects when the connected chain is not allowed.
- Optionally provide a small UI component for wrong-network messaging.
- Support triggering a network switch request when the wallet allows it.
- Document the recommended pattern in the Wallet documentation.

Expected behavior:
- The SDK clearly indicates when the user is connected to an unsupported network.
- The app can easily display which network is currently selected and which is expected.
- A “Switch network” action is available when supported by the wallet.
- If switching is unavailable or rejected, a friendly fallback message is shown.

### Describe alternatives you've considered.

_No response_

Start with the OnchainKit wallet components and the Wallet documentation mentioned in the issue, then identify the existing network and switch-request entry points. Add detection and switch behavior for Base and Base Sepolia, document the recommended pattern, and run a test covering wrong-network detection and switch requests, including unsupported or rejected switching.

Written by the indexing model from the issue text.