Chore: Improve Docker deployment configuration

- Use environment variables in docker-compose for secrets/paths
- Add .env.example template for required variables
- Add .env to .gitignore to prevent secret exposure
- Add docker-build-and-push.cmd helper script

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

.env.example

@@ -0,0 +1,13 @@
+# Docker image
+DOCKER_IMAGE=yourusername/moneymap:latest
+
+# Database connection
+DB_SERVER=your-server
+DB_USER=your-username
+DB_PASSWORD=your-password
+
+# OpenAI API key for receipt parsing
+OPENAI_API_KEY=your-openai-key
+
+# Host path for receipt storage
+RECEIPTS_HOST_PATH=/mnt/docker-data/moneymap/receipts