feat: coordinate multi-presenter remote sessions

[hrithik18k]

Summary

closes #2611

Adds multi-presenter coordination for remote synced sessions.

This introduces a shared active presenter driver so only one presenter publishes navigation updates to the synced audience deck at a time. Presenter views can see who is currently driving, request control, accept a handoff request, or take control immediately.

Changes

• Add shared activeDriver and driverRequest state for synced navigation sessions
• Guard presenter navigation publishing so inactive presenters cannot move the synced deck
• Guard presenter keyboard shortcuts when another presenter is active
• Add presenter toolbar controls for driver status, request handoff, accept request, and take over
• Support presenter labels via ?presenter= or ?driver=
• Document the multi-presenter remote workflow

Validation

• Ran changed-file ESLint successfully
• Full workspace vue-tsc --noEmit is currently blocked by unrelated VitePress declaration errors under docs/node_modules

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commit: efb7bab