What changes were proposed in this pull request?

This PR adds a loading skeleton/placeholder for the workflow definition list during data fetch operations, addressing issue #17948.

Changes:

• Added NSkeleton component from Naive UI to display loading placeholder
• Implemented conditional rendering to show skeleton during initial load, search, and pagination when no data exists
• Set table loading prop to false to prevent triggering global loading indicators
• Added comprehensive comments and documentation explaining the implementation

Implementation Details:

• Skeleton displays when loadingRef === true AND tableData is empty/null
• Skeleton repeat count matches page size for visual consistency
• Height set to 400px to accommodate multiple skeleton rows
• Uses Naive UI's animated shimmer effect

Benefits:

• Improved perceived performance with immediate visual feedback
• Better UX during slow network connections
• Clear distinction between loading, empty, and error states
• Isolated loading state (doesn't affect other components like navbar)

Related issue(s)

Closes #17948

Type of change

• New feature (non-breaking change which adds functionality)

Testing

• Tested skeleton display during initial page load
• Tested skeleton display during search with no results
• Tested skeleton display during pagination to empty pages
• Verified no global loading indicators are triggered
• Verified navbar/profile section is unaffected

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published