Add "Upgrade Available" banner and notifications integration

[DavidReque]

Description

Implement an "Upgrade Available" banner and notifications integration for the Dashboard frontend. The UI will inform users when a newer version is available and guide them to upgrade (without performing upgrades).

Background

The "Upgrade Available" feature is split into three parts: frontend, backend, and interface. This issue covers the frontend implementation.

Deliverables

// TODO

Requirements

• Don’t show immediately: wait 3–5 seconds after dashboard is ready
• If user closes banner: don’t show again for 24 hours
• If user selects “Don’t remind me”: store in localStorage and don’t show for that specific version
• Fail silently if version/GitHub data is unavailable (no banner)
• Cache version checks in localStorage for up to 12 hours (skip requests when cache is fresh; refresh when expired).