docs: refresh README demo GIF with updated VHS tape

[antomanc]

Summary

docs/assets/
- demo.tape (1100x680, 20fps, 16pt font)
+ demo.tape (1140x720, 30fps, 18pt JetBrains Mono, Catppuccin Mocha)
  # Interactive wizard walkthrough with slower, readable navigation
  # Captures Setup Summary (Money Shot #1) and 22/22 Doctor passing (Money Shot #2)
- demo.gif
+ demo.gif (711 KB, 30 FPS)

Evidence

• Before: Demo GIF from earlier version at 20 FPS / smaller canvas.
• After: High-resolution 30 FPS recording showcasing the full v2 interactive stack walkthrough and all 22 passing health checks.

Merge Danger

Door: two-way

Documentation asset update only.

Blast Radius: none

No runtime codebase impact.