Add updated logo for OP Mainnet (and OP Sepolia) network

### What is this about?

## **What is this about?**
Updating the official network icon for OP Mainnet and Testnet (OP Sepolia)

As part of a recent brand refresh, OP Mainnet (and testnet) has an updated logo to differentiate it from the Optimism Collective and the broader Superchain ecosystem. This issue requests the replacement of the existing network logo with the latest official version.

OP Mainnet Details:
- **Chain ID**: 10
- **RPC**: https://mainnet.optimism.io
- **Explorer**: https://optimistic.etherscan.io
- **Docs**: [OP Mainnet Network Details](https://docs.optimism.io/superchain/networks)

## **OP Sepolia Details**
- **Chain ID**: 11155420
- **RPC**: [https://sepolia.optimism.io](https://sepolia.optimism.io)
- **Explorer**: [https://sepolia-optimistic.etherscan.io](https://sepolia-optimistic.etherscan.io)
- **Docs**: [OP Sepolia Network Details](https://docs.optimism.io/superchain/networks)

Thank you very much!

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## **Scenario**
No response

## **Design**
Official network icon: Updated OP Mainnet and OP Sepolia Logo [here](https://deploy-preview-386--optimism-marketing-site.netlify.app/brand/op_mainnet_guidelines.zip)

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## **Technical Details**
No response

## **Threat Modeling Framework**
No response

## **Acceptance Criteria**

### 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


The issue provides an official logo archive and network identifiers for OP Mainnet and OP Sepolia, but names no repository file, entry point, or test. First locate the existing icons for chain IDs 10 and 11155420, then verify that replacement assets follow the linked brand guidance and display correctly in the extension.

Written by the indexing model from the issue text.