[Feature] Audience Q&A with Voting

[ariosavi]

Add a live Q&A system so the audience can ask and vote on questions during the presentation.

• Audience joins via QR code to submit questions.
• All questions are visible to others with upvote option.
• Presenter can view and highlight top questions.
• Final slide shows questions sorted by votes.

Blocked by

• [Feature] Add Speaker Mode #1
• [Feature] QR Code for Slides #2