Add Ollama fallback support to ai_fixer

Add Hugging Face Inference API fallback for AI fixer

Fix builtin syntax fixer for inline one-line headers and validate TGI fixes

Fix TGI endpoint plumbing and use full TGI runtime image in Dockerfile

Add TGI integration for cloud LLM serving

Finalizing CodeArena RL Benchmark: frontend improvements, GRPO training scripts, and cleaned environment