docs: clarify Zen fine-tune of Qwen3 audio base + honest base_model attribution

Add LICENSE and NOTICE files for license compliance

Add NOTICE: Copyright Zen Authors

Brand: remove upstream model references

fix(readme): frontmatter:tags+=['zen-3'] | body:stripped hf-download-Qwen prose

weights: server-side copy from Qwen/Qwen3-TTS-12Hz-1.7B-VoiceDesign

readme: initial Zen3 audio family member

initial commit