[Frontend] Build Carrier Marketplace Page

[mftee]

Description:
Build the marketplace page where carriers can browse all pending (available) shipments. Includes search by origin/destination and pagination.

Create frontend/app/(dashboard)/marketplace/page.tsx.

Acceptance Criteria:

• 'use client' directive
• Fetches shipmentApi.marketplace(params) on mount and on search submit
• Search bar: origin and destination text inputs + "Search" submit button + "Clear" button (visible when filters active)
• Search is form-submit triggered (not live/debounced)
• Shows loading skeleton (6 cards, 3-column grid) while fetching
• Empty state: "No available shipments right now. Check back soon!"
• Results in a 3-column grid on lg+, 2 on sm+, 1 on mobile using <ShipmentCard>
• Pagination controls (Previous / Page X of Y / Next) shown when totalPages > 1; Previous disabled on page 1; Next disabled on last page
• Shows total count below: "X shipment(s) available"
• On fetch error: toast.error()