feat(presentation): add multi-page event presentation with navigation

This commit introduces a complete multi-page presentation system for the 20251012 event.

Key features include:
- **Page Structure:** Establishes the page flow with an entry point, a main cover scene, a committee list, and
individual speech video pages.
- **Real-time Chroma Key:** Implements a canvas-based green screen effect to composite a video onto a background image.
A control panel allows for real-time adjustment of keying parameters, position, and scale.
- **Unified Navigation:** A new `nav.js` script enables seamless navigation between pages using keyboard (arrow keys,
Enter), touch swipes, and on-screen buttons. The navigation logic follows a predefined sequence (entry -> main ->
committee -> speeches).
- **Dynamic Content:** The committee list page dynamically generates its content from a JavaScript data source.

20251012/main.css

@@ -0,0 +1 @@
+@import "tailwindcss";