Add listings UI, components, and integrate frontend with backend services

[srilakshmi-anbarasan]

This PR adds the listings frontend UI and related components, and updates backend listing service integration.

Changes include:

• added listings page
• added ProductGrid, ProductCard, SortDropdown, FilterSection, and ListingStates components
• updated client app page
• updated backend app and listing service files
• updated package files as needed

[srilakshmi-anbarasan]

Updated the listings UI to match the seller management Figma design. Switched from category-based product grid to status-based layout (Active, Inactive, Drafts, Completed), added sidebar with counts, and refactored to a table-based view with row actions. Let me know if any styling or behavior should be adjusted further.