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/texture.hpp

@@ -30,9 +30,6 @@ enum class texture_type {
 };
 
 class texture {
-    GLuint m_id = 0;
-    texture_target m_target = texture_target::_2d;
-
 public:
     texture();
     explicit texture(texture_target target);
@@ -52,6 +49,10 @@ public:
     auto generate_mipmaps() -> void;
     auto id() const -> GLuint;
     auto valid() const -> bool;
+
+private:
+    GLuint m_id = 0;
+    texture_target m_target = texture_target::_2d;
 };
 
 }