Fix Dockerfile stages and dependencies

Dockerfile

@@ -1,4 +1,6 @@
-# Stage 1: Build your module
+# ==========================================
+# STAGE 1: Build Environment (Temporary)
+# ==========================================
 FROM python:3.10-slim AS builder
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
@@ -9,7 +11,9 @@ RUN apt-get update && apt-get install -y --no-install-recommends \
     && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app
-RUN pip install --no-cache-dir gradio numpy pypdf transformers torch --extra-index-url https://download.pytorch.org/whl/cpu
+
+# The builder ONLY needs pybind11 to compile the C++ code!
+RUN pip install --no-cache-dir pybind11
 
 # Copy only what your engine needs
 COPY CMakeLists.txt ./
@@ -20,13 +24,15 @@ RUN mkdir build && cd build && \
     cmake -DCMAKE_BUILD_TYPE=Release .. && \
     make vecmini
 
-# Stage 2: Final Runtime Environment
+# ==========================================
+# STAGE 2: Final Runtime Environment (Your App)
+# ==========================================
 FROM python:3.10-slim
 
 RUN useradd -m -u 1000 user
 WORKDIR /home/user/app
 
-# Install runtime math dependencies
+# Install runtime C++ math dependencies
 RUN apt-get update && apt-get install -y --no-install-recommends \
     libopenblas0 \
     libomp-dev \
@@ -37,7 +43,9 @@ COPY --from=builder /app/build/vecmini*.so /home/user/app/
 
 # Copy your frontend code (app.py)
 COPY --chown=user . /home/user/app
-RUN pip install --no-cache-dir gradio numpy
+
+# IMPORTANT: This is where ALL the runtime Python packages go!
+RUN pip install --no-cache-dir gradio numpy pypdf transformers torch --extra-index-url https://download.pytorch.org/whl/cpu
 
 ENV PORT=7860
 EXPOSE 7860