Enhance user management, improve API structure, add database optimizations, and update Docker setup

- Introduced endpoints for user management, including CRUD operations, pagination, and password management.
- Added new schema validations for user updates, password strength, pagination, and standardized error responses.
- Integrated custom exception handling for a consistent API error experience.
- Refined CORS settings: restricted methods and allowed headers, added header exposure, and preflight caching.
- Optimized database: added indexes on `is_active` and `is_superuser` fields, updated column types, enforced constraints, and set defaults.
- Updated `Dockerfile` to improve security by using a non-root user and adding a health check for the application.
- Enhanced tests for database initialization, user operations, and exception handling to ensure better coverage.

backend/Dockerfile

@@ -1,34 +1,66 @@
 # Development stage
 FROM python:3.12-slim AS development
+
+# Create non-root user
+RUN groupadd -r appuser && useradd -r -g appuser appuser
+
 WORKDIR /app
 ENV PYTHONDONTWRITEBYTECODE=1 \
     PYTHONUNBUFFERED=1 \
     PYTHONPATH=/app
+
 RUN apt-get update && \
-    apt-get install -y --no-install-recommends gcc postgresql-client && \
+    apt-get install -y --no-install-recommends gcc postgresql-client curl && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/*
+
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
+
 COPY . .
 COPY entrypoint.sh /usr/local/bin/
 RUN chmod +x /usr/local/bin/entrypoint.sh
+
+# Set ownership to non-root user
+RUN chown -R appuser:appuser /app
+
+# Switch to non-root user
+USER appuser
+
 ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]
 
 # Production stage
 FROM python:3.12-slim AS production
+
+# Create non-root user
+RUN groupadd -r appuser && useradd -r -g appuser appuser
+
 WORKDIR /app
 ENV PYTHONDONTWRITEBYTECODE=1 \
     PYTHONUNBUFFERED=1 \
     PYTHONPATH=/app
+
 RUN apt-get update && \
-    apt-get install -y --no-install-recommends postgresql-client && \
+    apt-get install -y --no-install-recommends postgresql-client curl && \
     apt-get clean && \
     rm -rf /var/lib/apt/lists/*
+
 COPY requirements.txt .
 RUN pip install --no-cache-dir -r requirements.txt
+
 COPY . .
 COPY entrypoint.sh /usr/local/bin/
 RUN chmod +x /usr/local/bin/entrypoint.sh
+
+# Set ownership to non-root user
+RUN chown -R appuser:appuser /app
+
+# Switch to non-root user
+USER appuser
+
+# Add health check
+HEALTHCHECK --interval=30s --timeout=10s --start-period=40s --retries=3 \
+    CMD curl -f http://localhost:8000/health || exit 1
+
 ENTRYPOINT ["/usr/local/bin/entrypoint.sh"]
 CMD ["uvicorn", "app.main:app", "--host", "0.0.0.0", "--port", "8000"]