✨ feat: Add skeleton loading states for sidebar navigation

Add comprehensive skeleton screen implementation for sidebar to improve loading UX, matching the existing headerbar skeleton pattern.

## Features Added
- **Sidebar skeleton screens**: Complete 1:1 recreation of sidebar structure during loading
- **Responsive skeleton layouts**: Different layouts for expanded (164×30px) and collapsed (44×44px) states
- **Skeleton component enhancements**: Extended SkeletonWrapper with new skeleton types (sidebar, button, sidebarNavItem, sidebarGroupTitle)
- **Minimum loading time**: Integrated useMinimumLoadingTime hook with 500ms duration for smooth UX

## Layout Specifications
- **Expanded nav items**: 164×30px with 8px horizontal margins and 3px vertical margins
- **Collapsed nav items**: 44×44px with 4px bottom margin and 8px horizontal margins
- **Collapse button**: 156×24px (expanded) / 36×24px (collapsed) with rounded corners
- **Container padding**: 12px top padding, 8px horizontal margins
- **Group labels**: 4px 15px 8px padding matching real sidebar-group-label styles

## Code Improvements
- **Refactored skeleton rendering**: Eliminated code duplication using reusable components (NavRow, CollapsedRow)
- **Configuration-driven sections**: Sections defined as config objects with title widths and item widths
- **Fixed width calculations**: Removed random width generation, using precise fixed widths per menu item
- **Proper CSS class alignment**: Uses real sidebar CSS classes (sidebar-section, sidebar-group-label, sidebar-divider)

## UI/UX Enhancements
- **Bottom-aligned collapse button**: Fixed positioning using margin-top: auto to stay at viewport bottom
- **Accurate spacing**: Matches real sidebar margins, padding, and spacing exactly
- **Skeleton stability**: Fixed width values prevent layout shifts during loading
- **Clean file structure**: Removed redundant HeaderBar.js export file

## Technical Details
- Extended SkeletonWrapper component with sidebar-specific skeleton types
- Integrated skeleton loading state management in SiderBar component
- Added support for collapsed state awareness in skeleton rendering
- Implemented precise dimension matching for pixel-perfect loading states

Closes: Sidebar skeleton loading implementation

web/src/components/table/models/modals/UpstreamConflictModal.jsx

@@ -91,6 +91,7 @@ const UpstreamConflictModal = ({
       {
         title: t('模型'),
         dataIndex: 'model_name',
+        fixed: 'left',
         render: (text) => <Text strong>{text}</Text>,
       },
     ];
@@ -235,7 +236,12 @@ const UpstreamConflictModal = ({
           <div className='mb-3 text-[var(--semi-color-text-2)]'>
             {t('仅会覆盖你勾选的字段，未勾选的字段保持本地不变。')}
           </div>
-          <Table columns={columns} dataSource={dataSource} pagination={false} />
+          <Table
+            columns={columns}
+            dataSource={dataSource}
+            pagination={false}
+            scroll={{ x: 'max-content' }}
+          />
         </>
       )}
     </Modal>