Add entrypoint script for Docker container

Introduces entrypoint.sh to handle database migrations before starting the Flask app. Updates Dockerfile to use the new entrypoint script and ensures it is executable.

entrypoint.sh

@@ -0,0 +1,8 @@
+#!/bin/sh
+set -e
+
+echo "Running database migrations..."
+flask db upgrade
+
+echo "Starting Flask app..."
+python app.py