feat: add server-side search, filtering, and sorting to product listing

[bh462007]

Fixes #424.

This PR adds server-side filtering, keyword search, and sorting to GET /api/product/list while preserving the existing pagination behavior.

Changes

backend/controller/productController.js (listProducts())

• Added optional query parameters:
  • category
  • subCategory
  • minPrice
  • maxPrice
  • search
  • sort
• Builds the MongoDB query dynamically so multiple filters can be combined.
• Added case-insensitive product name search using $regex.
• Added sorting options:
  • price_asc
  • price_desc
  • newest
• Falls back to the existing insertion-order sorting when no valid sort option is provided.
• Updated pagination metadata (total and pages) to reflect filtered results.
• Existing requests without query parameters continue to behave exactly as before.

Example Requests

GET /api/product/list?category=Men&subCategory=Topwear&minPrice=500&maxPrice=2000&search=jacket&sort=price_asc&page=1&limit=20

GET /api/product/list?sort=price_desc

GET /api/product/list?search=jacket

Testing

Verified locally that:

• ✅ Category and subcategory filtering return only matching products.
• ✅ Price range filtering correctly includes and excludes products.
• ✅ Search is case-insensitive.
• ✅ Sorting works correctly for all supported options.
• ✅ Multiple filters work together.
• ✅ Pagination metadata reflects filtered results.
• ✅ Existing pagination behavior remains unchanged when no filters are supplied.

Notes

• Search currently uses a case-insensitive $regex. A MongoDB text index ($text) can be considered later for larger catalogs.
• Database indexes for category, subCategory, and price are intentionally left as a follow-up optimization.

Branch Note

This branch is based on fix/415-index-startup-crash because main currently cannot start due to #415. Once that PR is merged, this branch can be rebased onto the updated main before merging.

Checklist

• Supports category, subCategory, minPrice, maxPrice, search, and sort
• Multiple filters work together
• Pagination metadata reflects filtered results
• Backward compatible when no query parameters are provided
• Verified search, filtering, and sorting locally
• Database indexes (follow-up improvement)

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[Nsanjayboruds]

@bh462007 fix the lint backend