feat: ZeroGPU backend for Hugging Face Spaces deployment (#4)

fix: use Hugging Face inference on Space

Refactor stage 4 script generation: implement story deduplication, guide segues with transition instructions, and configure NotebookLM-style long-form prompts with strict turn constraints (#2)

feat: SmolLM2-135M ranker fine-tuning pipeline + BAML streaming improvements

feat: migrate rank + script stages to BAML typed prompts