add delivery radius updates

[parinaB]

[Feature Add] Enhanced Delivery Radius Validation with Real-Time Eligibility Feedback

🔗 Related Issue

Closes #72

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🧩 Problem

The previous checkout flow had zero delivery radius validation — clicking "Place Order" would immediately confirm any order regardless of the user's location. There was no feedback, no location check, and no error handling.

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✅ What This PR Does

Introduces a complete delivery eligibility system triggered at checkout:

• 📍 Fetches user's real-time GPS coordinates via the Geolocation API
• 📐 Calculates Haversine distance from the restaurant origin
• 🟢 Within 5 km → eligible, order proceeds
• 🟠 5–8 km → blocked with a "just outside range" message
• 🔴 Beyond 8 km → blocked with a clear area-not-served message
• ⚠️ Handles all edge cases: permission denied, GPS unavailable, request timeout
• 🔘 Checkout button disables + shows "Checking location..." during async check
• Inline styled status block replaces all alert() calls for delivery feedback

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📁 Files Changed

File	Change
js/main.js -> Added haversineDistance(), getDeliveryZone(), checkDeliveryEligibility(), showDeliveryStatus() — replaced window.checkout with async guarded version
cart.html --> Added <div id="delivery-status" aria-live="polite"> above checkout button

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📸 Screenshots

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🧪 How to Test

1. Add items to cart
2. Click Place Order
3. Allow location when prompted
4. Observe inline delivery status message
5. To test rejection: deny location permission → error message appears

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📝 Notes

• Restaurant coordinates are currently a placeholder (to be updated by maintainer)
• Uses maximumAge: 60000 to avoid redundant GPS calls on repeat attempts
• Orange theme preserved throughout; no style regressions
• Fully accessible — status block uses aria-live="polite"

[parinaB]

@PatelHarsh2006 any reviews or updates?