Accessibility issue: Semantic HTML, heading structure, and layout cleanups on /

[github-actions]

Consolidated accessibility scanning findings for / page:

• Buttons must have discernible text (originally Accessibility issue: Semantic HTML, heading structure, and layout cleanups on / #2688)
• Table header text should not be empty (originally Accessibility issue: Table header text should not be empty on / #2689)
• Document should have one main landmark (originally Accessibility issue: Document should have one main landmark on / #2690)
• Links must have discernible text (originally Accessibility issue: Links must have discernible text on / #2691)
• Page should contain a level-one heading (originally Accessibility issue: Page should contain a level-one heading on / #2692)
• All page content should be contained by landmarks (originally Accessibility issue: All page content should be contained by landmarks on / #2693)

Closes #2689, #2690, #2691, #2692, #2693.