- Add documentation comments to all AVTransport, RenderingControl & ConnectionManager handlers
- Simplify play_handler: remove redundant state writes and clarify flow with comments
- Deduplicate pipeline command logic in registry.rs by introducing send_pipeline_command helper
- Replace direct PlayerCommand usage with unified PipelineControl enum in registry and handlers
- Fix handler signatures: clone pipeline once before Arc closure (next/previous)—avoid redundant clones
- Add helper macros for UPnP service factory to reduce boilerplate (add_action, add_var)
- Minor formatting fixes: sort imports and align handler assignments