refactor Dockerfile: streamline build process by removing builder stage and consolidating dependency installation

Dockerfile

@@ -1,39 +1,28 @@
 ARG BASE_IMAGE=ghcr.io/meta-pytorch/openenv-base:latest
 
-# -------- BUILDER STAGE --------
-FROM python:3.12-slim AS builder
+FROM ${BASE_IMAGE}
 
 WORKDIR /app
 
+# Build tools needed for pandas/numpy/scikit-learn C extensions
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
-        git curl build-essential \
+        git build-essential \
     && rm -rf /var/lib/apt/lists/*
 
+# Copy source
 COPY . /app/env
-WORKDIR /app/env
-
-# Install all deps except openenv (which lives in the base image)
-RUN --mount=type=cache,target=/root/.cache/pip \
-    grep -v 'openenv' requirements.txt | \
-    pip install --target /app/packages -r /dev/stdin
-
-
-# -------- RUNTIME STAGE --------
-FROM ${BASE_IMAGE}
-
-WORKDIR /app
 
-COPY --from=builder /app/env /app/env
-COPY --from=builder /app/packages /app/packages
+# Install directly into the base image's own Python — no venv, no --target
+# openenv is already provided by the base image, so exclude it
+RUN grep -v 'openenv' /app/env/requirements.txt | pip install -r /dev/stdin
 
-# Download NLTK data
-RUN PYTHONPATH=/app/packages python -m nltk.downloader \
+# Download NLTK data — nltk is now properly installed, so this just works
+RUN python -m nltk.downloader \
         wordnet omw-1.4 stopwords punkt \
         averaged_perceptron_tagger_eng punkt_tab
 
-# /app/packages first so our versions win; openenv comes from base image's site-packages
-ENV PYTHONPATH="/app/packages:/app/env:$PYTHONPATH"
+ENV PYTHONPATH="/app/env:$PYTHONPATH"
 
 HEALTHCHECK --interval=30s --timeout=3s --start-period=5s --retries=3 \
     CMD curl -f http://localhost:7860/health || exit 1