containerfile: fix jaraco.context CVE and consolidate

- explicitly install jaraco.context>=6.1.0 in runtime stage
  to override vendored copy in setuptools (GHSA-58pv-8j8x-9vj2)
- remove redundant installs from builder (requirements.txt
  already pins setuptools>=80.0 and jaraco.context>=6.1.0)
- consolidate runtime pip install into single command
- remove redundant comments

Containerfile

@@ -7,18 +7,16 @@ FROM python:3.11-slim AS builder
 
 WORKDIR /build
 
-# Install build dependencies and clean up
+# Install build dependencies
 RUN apt update && apt install -y --no-install-recommends gcc \
-    && apt clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/*
+    && apt clean && rm -rf /var/lib/apt/lists/*
 
-# Create virtual environment
+# Create virtual environment and upgrade pip
 RUN python -m venv /opt/venv
 ENV PATH="/opt/venv/bin:$PATH"
+RUN pip install --no-cache-dir --upgrade pip wheel
 
-# Upgrade pip/setuptools first (pulls in security-fixed jaraco.context)
-RUN pip install --no-cache-dir --upgrade pip setuptools wheel
-
-# Install Python dependencies
+# Install Python dependencies (includes security pins for setuptools, jaraco.context)
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt gunicorn
 
@@ -29,19 +27,19 @@ FROM python:3.11-slim
 LABEL maintainer="FlaskPaste"
 LABEL description="Lightweight secure pastebin REST API"
 
-# Clean base image caches, upgrade system pip/setuptools, create non-root user
+# Cleanup base image, fix base image vulnerabilities, create non-root user
+# Note: System packages upgraded for Trivy scan; app runs from venv
 RUN apt clean && rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* \
-    && pip install --no-cache-dir --upgrade pip setuptools \
+    && pip install --no-cache-dir --upgrade pip 'setuptools>=80.0' 'jaraco.context>=6.1.0' \
     && groupadd -r flaskpaste && useradd -r -g flaskpaste flaskpaste
 
 # Copy virtual environment from builder
 COPY --from=builder /opt/venv /opt/venv
 ENV PATH="/opt/venv/bin:$PATH"
 
-# Set working directory
 WORKDIR /app
 
-# Copy only necessary application files
+# Copy application files
 COPY app/ ./app/
 COPY wsgi.py .
 COPY fpaste .
@@ -49,7 +47,6 @@ COPY fpaste .
 # Create data directory with correct ownership
 RUN mkdir -p /app/data && chown -R flaskpaste:flaskpaste /app
 
-# Switch to non-root user
 USER flaskpaste
 
 # Environment defaults
@@ -58,12 +55,9 @@ ENV FLASKPASTE_DB=/app/data/pastes.db
 ENV PYTHONUNBUFFERED=1
 ENV PYTHONDONTWRITEBYTECODE=1
 
-# Expose port
 EXPOSE 5000
 
-# Health check
 HEALTHCHECK --interval=30s --timeout=5s --start-period=5s --retries=3 \
     CMD python -c "import urllib.request; urllib.request.urlopen('http://localhost:5000/health')" || exit 1
 
-# Run with gunicorn
 CMD ["gunicorn", "--bind", "0.0.0.0:5000", "--workers", "2", "--access-logfile", "-", "wsgi:application"]