Fix web fullscreen sizing and stability

[fcarucci]

Summary

Fixes WebAssembly/WebGPU fullscreen behavior on web builds so rendering remains stable and fills the screen.

Changes

• Added proper web fullscreen handling in thirteen.h (PlatformWeb):
  • Request fullscreen via emscripten_request_fullscreen_strategy.
  • Fallback to soft fullscreen if needed.
  • Handle fullscreen enter/exit with CSS updates so canvas fills viewport.
• Improved WebGPU surface robustness during fullscreen transitions:
  • Recreate/reconfigure surface when texture acquisition fails.
  • Keep render path resilient to transient canvas/surface state changes.
• Removed unsupported wgpuSurfacePresent usage in web runtime path.
• Kept all fixes inside thirteen.h (no example source changes).

Validation

• Rebuilt WASM sample with:
  • emcc Examples/Simple/main.cpp -std=c++17 -I. --use-port=emdawnwebgpu -sASYNCIFY -sALLOW_MEMORY_GROWTH=1 -o /tmp/thirteen_simple.html
• Verified fullscreen no longer blacks out and canvas fills screen in Chrome