Add MOSS community full-checkpoint support
Implementation details:
- Add the LAION MOSS-TTS v1.5 Voice Acting 8B community model to the engine dropdown and downloader
- Discover compatible local MOSS full checkpoints and resolve architecture from config.json
- Enable the LAION Delay checkpoint in the existing LoRA training pipeline
- Reject unsupported local MOSS layouts instead of assuming Local Transformer
- Address issue #340