Add index on collections field for performance improvement

[sorabhlahoti]

Description

Added an index on the collections field in the Product schema to improve query performance for the /api/collections/:name endpoint.
Closes #101

Type of Change

• Bug fix
• New feature
• Documentation update
• Refactor
• Other (please describe):

Checklist

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code where necessary
• I have updated documentation (README, Usage, etc.)
• My changes generate no new warnings or errors
• I have added tests (if applicable)
• All tests pass locally with my changes

[Alexandrbig1]

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[Alexandrbig1]

@sorabhlahoti, congratulations on your merged PR! 🎉 Don’t forget to add yourself as a contributor using our all-contributors bot. You can find instructions in our CONTRIBUTING.md. Thanks again for your contribution!

[Alexandrbig1]

Hey @sorabhlahoti ,

🎉 Congratulations on your first merged pull request!
You’ve just taken a huge step in your open-source journey — and we’re so excited it happened here at Open Code Chicago × CoreX 💪

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[Alexandrbig1]

Hey @sorabhlahoti ,

🔥 Congratulations — your backend contributions have been outstanding!
Your work on the CoreX Project has strengthened our foundation, improved functionality, and helped bring our open source vision to life during Hacktoberfest 2025.

You’ve officially earned the Backend Engineer 2025 badge from Open Code Chicago × CoreX 🏅
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Thank you for writing clean, secure, and efficient code that powers our project behind the scenes.
Your expertise keeps everything running smoothly 🚀

— The Open Code Chicago Team