SEARCH-057: [Search] Search Dropdown Results UI

[0xfynnix]

Implement search results dropdown list UI with keyboard navigation support.
Display different icons and indicators for different types of search results.

• Display search results dropdown below input
• 500ms debounce handling
• Support ↑/↓ keyboard navigation
• Enter selects current item and navigates
• Esc closes dropdown
• Click outside closes dropdown
• Loading state shows spinner
• No results shows "No Results"
• Account: User icon
• Transaction: Transaction icon
• Block: Block icon
• Coin: Display token logo
• Group results by type (optional)