style: move public members first in class declarations

- Reorder all class headers to put public interface before private members
- Document convention in AGENTS.md

cbt/opengl/descriptor.hpp

@@ -16,14 +16,15 @@ struct descriptor_binding {
 };
 
 class descriptor_set {
-    std::vector<descriptor_binding> m_bindings;
-
 public:
     descriptor_set();
     auto add_texture(texture tex, GLuint unit = 0) -> void;
     auto add_buffer(buffer buf, GLuint unit = 0) -> void;
     auto bind_all() -> void;
     auto count() const -> size_t;
+
+private:
+    std::vector<descriptor_binding> m_bindings;
 };
 
 }