fix: update schema to fix multiple primary key issues and switch to node-postgres

- Replace primaryKey constraints with uniqueIndex where needed
- Fix schema for Auth, Contacts, Exchange Rates, Expense Participants, and Accounts tables
- Add missing import for uniqueIndex
- Switch from postgres.js to node-postgres (pg) for Drizzle
- Add proper type safety with TypeScript
- Add graceful shutdown of database connections

backend/Dockerfile

@@ -0,0 +1,38 @@
+FROM oven/bun:1.2 as base
+
+# Set working directory
+WORKDIR /app
+
+# Copy package files
+COPY package.json bun.lock ./
+
+# Install dependencies
+RUN bun install --frozen-lockfile
+
+# Copy source code
+COPY . .
+
+# Set environment variables
+ENV NODE_ENV=production
+ENV PORT=3000
+
+# Expose port
+EXPOSE 3000
+
+# Start the application
+CMD ["bun", "run", "start"]
+
+# Development stage
+FROM base as development
+
+# Override environment variables for development
+ENV NODE_ENV=development
+
+# Start development server
+CMD ["bun", "run", "dev"]
+
+# Migration stage
+FROM base as migration
+
+# Run migrations
+CMD ["bun", "run", "db:migrate"]