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/locales/en.ts

@@ -1442,6 +1442,7 @@ This delimiter is used to split the input text into several text pieces echo of
       showQueryMindmap: 'Show Query Mindmap',
       embedApp: 'Embed App',
       relatedSearch: 'Related Search',
+      descriptionValue: 'You are an intelligent assistant.',
       okText: 'Save',
       cancelText: 'Cancel',
     },

web/src/locales/zh.ts

@@ -1345,6 +1345,7 @@ General：实体和关系提取提示来自 GitHub - microsoft/graphrag：基于
       showQueryMindmap: '显示查询思维导图',
       embedApp: '嵌入网站',
       relatedSearch: '相关搜索',
+      descriptionValue: '你是一位智能助手。',
       okText: '保存',
       cancelText: '返回',
     },