Added coming-soon page for the broken route

[ankithajv]

📝 Pull Request Template

📄 Description

This PR addresses the issue where clicking on unfinished features (like "Terms" or "Shop") resulted in a broken 404 error page.

Changes implemented:

1. Created coming_soon.php: A responsive, "Foodogram-themed" placeholder page with a cooking metaphor ("We're still cooking this up! 🍳").
2. Added router.php: A script that intercepts 404 errors and redirects users to the Coming Soon page automatically, so we don't need to create empty files for every missing feature.
3. Fixed Navigation Links: Updated the Sidebar and Footer links to use absolute paths (e.g., /pages/about.php) to resolve the "Not Found" errors when navigating between the Home page and sub-pages.

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🔗 Related Issues

Fixes #<insert_your_issue_number_here>
(Check your GitHub Issues tab to find the number, e.g., #2)

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🧩 Type of Change

• 🐛 Bug Fix (Fixed broken menu links and 404 errors)
• ✨ New Feature (Added "Coming Soon" page)
• ⚡ Enhancement / Optimization
• 🧾 Documentation Update

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🖼️ Screenshots

Recording.2026-01-29.194134.mp4

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✅ Checklist

• I have performed a self-review of my code.
• I have tested my changes locally.
• My changes do not break existing functionality.
• I have linked all related issues.

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[ankithajv]

@Mrigakshi-Rathore , I have done it for all pages which show 404 error!