docs: honest base_model attribution, drop marketing

Add LICENSE and NOTICE files for license compliance

Add NOTICE: Copyright Zen Authors

fix(readme): frontmatter:library_name,tags+=['hanzo'] | body:sub('\\| \\[Zen Max\\]\\(https://huggingface\\.co/zenlm/zen-max\\)[^\\n]*\\n')x1

Update model card: fix YAML tags, add zen/zenlm branding

Update model card: add zen/zenlm tags, fix branding

Update README: Zen Reranker branding and model card

Duplicate from Qwen/Qwen3-Reranker-4B