feat(gpu): Systematize post-process bindings and enable vertex shader uniforms

- Add PP_BINDING_* macros for standard post-process bind group layout
  - PP_BINDING_SAMPLER (0): Input texture sampler
  - PP_BINDING_TEXTURE (1): Input texture from previous pass
  - PP_BINDING_UNIFORMS (2): Custom uniforms buffer
- Change uniforms visibility from Fragment-only to Vertex|Fragment
  - Enables dynamic geometry in vertex shaders (e.g., peak meter bar)
- Replace all hardcoded binding numbers with macros in post_process_helper.cc
- Update test_demo.cc to use systematic bindings
- Benefits: All post-process effects can now access uniforms in vertex shaders

Result: More flexible post-process effects, better code maintainability

0 files changed, 0 insertions, 0 deletions