Fixes (web): Optimized search page style and functionality #3221 (#9627)

### What problem does this PR solve?

Fixes (web): Optimized search page style and functionality #3221

- Updated search page and view title styles
- Modified dataset list and multi-select control styles
- Optimized text field and button styles
- Updated filter button icons
- Adjusted metadata filter styles
- Added default descriptions for the smart assistant

### Type of change

- [x] Bug Fix (non-breaking change which fixes an issue)

web/src/pages/next-search/search-home.tsx

@@ -27,7 +27,7 @@ export default function SearchPage({
       <div className="relative z-10 px-8 pt-8 flex  text-transparent flex-col justify-center items-center w-[780px]">
         <h1
           className={cn(
-            'text-4xl font-bold bg-gradient-to-r from-sky-600 from-30% via-sky-500 via-60% to-emerald-500 bg-clip-text',
+            'text-4xl font-bold bg-gradient-to-l from-[#40EBE3] to-[#4A51FF] bg-clip-text',
           )}
         >
           RAGFlow