Two fixes:

1. README not visible in HF Space's playground UI ('No README available'
shown to visitors). OpenEnv's gradio_ui.py reads README from
/app/README.md by default, but our Dockerfile copies the repo to
/app/env/, so the README lookup failed.

Fix: set ENV_README_PATH=/app/env/README.md in the Dockerfile, which
the OpenEnv web_interface.py reads as a fallback path.

2. Root Dockerfile was UTF-16 LE with BOM (FF FE prefix) which is
correct enough for Docker but fragile and inconsistent with all
other text files in the repo (UTF-8). Re-encoded as UTF-8/ASCII.
Functional content unchanged from server/Dockerfile counterpart.