fix: Gradio mount, verifier stage3, poc_history clear, real notebook

rewrite: training notebook - drop Unsloth, use transformers+peft+bitsandbytes

feat: GRPO training, fixed curriculum stages 2+3, AST verifier, leaderboard UI, openenv schema

fix: remove 3 debug cells from notebook

feat: add real training notebook from Colab run

initial deploy — jairaj files, teammate files pending