fix(controls): Prevent keyboard focus on hidden buttons in ContentDialog

[apachezy]

Pull request type

Please check the type of change your PR introduces:

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the current behavior?

When primary/secondary buttons in ContentDialog have no content, they are only visually hidden by setting their parent grid column width to zero. However, the buttons themselves remain accessible via Tab focus, can still be activated by Enter/Space keys, and may be detected by screen readers and other assistive tools.

Issue Number: N/A

What is the new behavior?

• Primary/secondary buttons with no content are now properly disabled and collapsed
• Buttons without content can no longer receive focus via Tab navigation or be activated by Enter/Space keys
• Buttons without content are now properly ignored by assistive tools