Refactor Dockerfile to optimize layer caching and ensure proper user permissions

Dockerfile

@@ -1,15 +1,23 @@
 FROM python:3.9-slim
 
-# Create app user and directory
-RUN useradd -m appuser && mkdir -p /app && chown appuser:appuser /app
+# Install system dependencies first as root
+RUN apt-get update && apt-get install -y --no-install-recommends \
+    gcc python3-dev \
+    && rm -rf /var/lib/apt/lists/*
 
 WORKDIR /app
 
-# Copy files with proper ownership
-COPY --chown=appuser:appuser . .
-
-USER appuser
+# Copy requirements first for caching
+COPY requirements.txt .
 
+# Install Python dependencies system-wide
 RUN pip install --no-cache-dir -r requirements.txt
 
+# Copy application files
+COPY . .
+
+# Create non-root user and set permissions
+RUN useradd -m appuser && chown -R appuser:appuser /app
+USER appuser
+
 CMD ["uvicorn", "main:app", "--host", "0.0.0.0", "--port", "7860"]