Resolve "Style labels on Issue Finder page"

• Please check this box if this contribution uses AI-generated content (including content generated by GitLab Duo features) as outlined in the GitLab DCO & CLA. As a benefit of being a GitLab Community Contributor, you receive complimentary access to GitLab Duo.

What does this MR do and why?

This MR implements pill badge styling for issue labels on the Issue Finder page to improve visual consistency and user experience.

• Replaced plain text labels with Bootstrap Vue's BBadge components using pill and variant="secondary" properties
• Added comprehensive test coverage to ensure proper rendering and filtering behavior

Screenshots or screen recordings

Before	After

Validation steps

1. Navigate to the Issue Finder page:

• Open http://localhost:3030/issues in your browser
• Verify the page loads without errors

2. Verify Issue Display Section (DisplaySection):

• Confirm issues are grouped by category in an accordion format
• Check that each issue's labels appear as pill badges below the issue title
• Verify badges have consistent styling (rounded corners, gray background)

/cc @leetickett-gitlab

Closes #246 (closed)