refactor: migrate from SQLite to PostgreSQL for session management and data storage

- Updated package dependencies to replace SQLite with PostgreSQL.
- Modified privacy policy to reflect the change in database technology.
- Adjusted session management in server.js to use connect-pg-simple.
- Enhanced docker-compose.yml to include PostgreSQL service with health checks.
- Added Dockerfile for multi-stage builds for development and production environments.
- Introduced .dockerignore to exclude unnecessary files from the Docker context.

Dockerfile

@@ -0,0 +1,14 @@
+FROM node:20-bookworm-slim AS development
+WORKDIR /app
+COPY app/package*.json ./
+RUN npm install
+COPY app/ ./
+CMD ["node", "server.js"]
+
+FROM node:20-bookworm-slim AS production
+ENV NODE_ENV=production
+WORKDIR /app
+COPY app/package*.json ./
+RUN npm install --omit=dev && npm cache clean --force
+COPY app/ ./
+CMD ["node", "server.js"]