ux: Add a "Clear Cache" developer utility button in the footer

[AlAfiz]

Description

During development and Beta testing, local storage and cached API responses can cause the UI to break or display stale data.
Asking users to manually dig into their browser dev tools to clear storage is bad UX.
We need a small, subtle "Clear App Data" button hidden in the footer for quick resets.
This will save massive amounts of time during QA testing for Wave 3.

Requirements

• Add a small text link to the Footer.tsx component labeled "Clear Cache".
• Attach an onClick handler that calls localStorage.clear().
• Trigger a simple browser alert("App data cleared. Please refresh the page.") after clearing.
• Ensure the button uses a subtle text color so it doesn't distract from the main links.