Add search functionality

[raggopaluni]

Description

Neighbor types → sees matching products and services instantly.

Searches: product name, description, category, service name, tags.
Filtered by current neighborhood.
300ms debounce. Results as they type.

Use Supabase full text search — no extra tech needed.

Acceptance Criteria

• Results appear as user types
• Searches products and services
• Respects neighborhood filter
• Empty state if no results
• Tracks search_query in GA4
• Clears on X button

Dependencies

Issues #15, #16