updated with new videos and news item

[jaydestro]

This pull request updates conference agenda data, video URLs, and speaker/session details, as well as adds a new news item about the Skills Challenge. The main focus is on improving how speaker video URLs are selected, updating session metadata, and ensuring accurate, up-to-date information for attendees.

Agenda and video updates:

• Improved the getVideoUrlForSpeaker function in videoRelease.ts to prefer sessions where the speaker is the sole presenter, falling back to multi-speaker sessions only if necessary. This ensures that links for speakers point to their main talk when available.
• Updated session video URLs in agenda.json:
  • Added a YouTube URL for the "Andrew Liu, Steve Berg" session.
  • Changed the video URL for "Behind the Scenes: How Azure Cosmos DB Runs Under the Hood" to a new YouTube link.
  • Added a new session: "Keynote Interview: AMD's Steve Berg on the Hardware Behind Cosmos DB," including its YouTube URL.

Speaker/session metadata:

• Updated Steve Berg's session title and abstract in speakers2026.json to reflect the new keynote interview, providing a more detailed and accurate session description.

News and announcements:

• Added a new news item in news.json about the Skills Challenge, highlighting its extension through May 8, 2026, and details on how to participate and submit entries.