Implement Kleo extension sidepanel screens

[CodecCods]

Summary

• Implement the four requested extension sidepanel screens from Kleo Network Extension Screens (React) #26: account create/import, task list, wallet, and settings.
• Add local account persistence so the sidepanel can move from onboarding into the tabbed experience without storing the private key.
• Add Chrome side_panel manifest support while keeping the existing popup entrypoint.
• Update the existing CRA smoke test for the new UI.

Testing

• npm run build
• npx react-scripts test --watchAll=false

Closes #26.

Note: I saw the old Dec 2024 claim comment, but there is no linked PR or follow-up activity visible, so I opened this complete implementation for review.