cat2151/mmlabc-to-smf-rust

AI Summary: This issue proposes enhancing the UI of the `mmlabc-to-smf-gui` demo application. It aims to improve readability by adding collapse buttons to all display fields, making them collapsed by default, and converting the JSON result display field into an editable text area for easier copying. These changes will be applied to the main demo, while ensuring the `demo-library` remains simple and unaffected.

AI Summary: This issue proposes implementing support for the special `@128` instrument in mmlabc, which signifies a General MIDI drum track. The `mmlabc-to-smf-rust` converter must assign tracks containing `@128` to MIDI channel 9 (0-based) and ensure this designation takes precedence over other instrument specifications within the same track. It also requires careful handling of program change events, which are typically ignored on drum channels, to conform to both mmlabc and General MIDI conventions.

AI Summary: This issue proposes improving `README.ja.md` by removing direct grammar descriptions. Instead, it will replace them with URL links pointing to `src/grammer.js`, making `src/grammer.js` the Single Source of Truth for grammar. This ensures readers always access the most current and accurate grammar information.