add loading spinner while fetching food listingsFeature/loading spinner

[Gowthamimudam]

📌 What’s Changed

This PR adds a loading spinner that appears while food listings are being fetched from the database. Previously, there was no loading indicator, which could confuse users on slow networks.

✅ Improvements

• Shows a spinner centered on screen while data is loading
• Ensures spinner stays visible for at least 300ms to avoid flickering
• Adds dimmed background during load to improve perceived performance
• Spinner hides automatically when data has finished loading
• Refactors loadListingsFromDB() in foodlisting.js to manage spinner state

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[Gowthamimudam]

Hello @angelabera ,I have resolved the merge conflits and added the feature please go through it and add a difficulty badge swoc 2026.