feat(shaders_lab): uniform annotations → auto-generated ImGui controls

- cpp/functions/gfx/uniform_parser: regex-based parser of @slider/@color/@toggle/@xy annotations (+ inline tests)
- cpp/functions/gfx/uniform_panel: ImGui widgets + value store + glUniform* apply
- shader_canvas: optional uniforms callback invoked per-frame
- gl_loader: +glUniform1i/3f/4f
- seed plasma: demo uniforms u_speed + u_color
- rebuild Windows .exe

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

cpp/functions/gfx/gl_loader.cpp

@@ -26,7 +26,10 @@ PFNGLGETUNIFORMLOCATIONPROC  fn_glGetUniformLocation  = nullptr;
 PFNGLLINKPROGRAMPROC         fn_glLinkProgram         = nullptr;
 PFNGLSHADERSOURCEPROC        fn_glShaderSource        = nullptr;
 PFNGLUNIFORM1FPROC           fn_glUniform1f           = nullptr;
+PFNGLUNIFORM1IPROC           fn_glUniform1i           = nullptr;
 PFNGLUNIFORM2FPROC           fn_glUniform2f           = nullptr;
+PFNGLUNIFORM3FPROC           fn_glUniform3f           = nullptr;
+PFNGLUNIFORM4FPROC           fn_glUniform4f           = nullptr;
 PFNGLUSEPROGRAMPROC          fn_glUseProgram          = nullptr;
 
 namespace fn::gfx {
@@ -60,7 +63,10 @@ bool gl_loader_init() {
     LOAD(glLinkProgram);
     LOAD(glShaderSource);
     LOAD(glUniform1f);
+    LOAD(glUniform1i);
     LOAD(glUniform2f);
+    LOAD(glUniform3f);
+    LOAD(glUniform4f);
     LOAD(glUseProgram);
 
     #undef LOAD