Fix keyboard focus order in the SDK installer

[Copilot]

The installer placed keyboard focus on a static success heading and announced descriptive content with the “Learn more” link.

• Success screen
  • Remove the non-interactive success heading from the tab order.
• Installation screen
  • Render the description as a static label.
  • Keep only the “Learn more” hypertext control keyboard-focusable.

• Fixes Keyboard focus moves to "Installation Successfully Completed" text after close button but focus indicator is not visible.:Screen reader announces surrounding content along with "Learn more" link.: A11y_ .NET SDK and CLI_InstallationScreen_Keyboard #55634

[azure-pipelines]

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[joeloff]

There might be fallout here around accessibility and screen readers. This will require handing off a private build for assessment to ensure nothing is being regressed.

[joeloff]

The Installation Successfully Completed text is not read out loud by Narrator. Verified against 10.0.400 that the text is being read.

I reached out to the CAI channel - the code change is fine. Pretty sure we fixed this during the AI pass in 10 when the text wasn't being read, so this fix would technically be a regression. We can have one or the other, but not both.