Replace deprecated KeyboardControlModifier with platform-aware primary modifier
handling. Introduces KeyboardMetaModifier for native modifier keys (Cmd on macOS,
Win on Windows, Super on X11) and KeyboardPrimaryModifier to abstract the
platform-specific primary modifier key. Adds isPrimaryModifierOnly() helper
to normalize platform differences in keyboard shortcuts.
Extract Cocoa view handling into separate OTOpenGLView and OTWindowDelegate
classes for improved code organization and maintainability.
