chore: update HF Space to Python 3.12, unpin gradio

- hf_space/Dockerfile: 3.10-slim → 3.12-slim to match dev env and Lambda
- hf_space/requirements.txt: remove gradio version pin
- environment.yml: remove gradio version pin

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Dockerfile

@@ -1,4 +1,4 @@
-FROM python:3.10-slim
+FROM python:3.12-slim
 
 RUN apt-get update && apt-get install -y \
     build-essential \

requirements.txt

@@ -1,4 +1,4 @@
-gradio==5.43.0
+gradio
 datasets
 huggingface_hub
 gradio-leaderboard