fix: HF Space port + TRL install order in training Dockerfile

- README: add app_port: 8000 so HF Space routes traffic correctly
- training/Dockerfile: install TRL last with --upgrade to avoid
unsloth pinning it to a version incompatible with vllm 0.12.0

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

README.md

@@ -4,6 +4,7 @@ emoji: 🤖
 colorFrom: blue
 colorTo: purple
 sdk: docker
+app_port: 8000
 pinned: false
 ---