feat: add multi-stage Dockerfile and enhanced docker-compose deployment guide

[sakshar2303]

Summary

This PR addresses Issue #4 by providing a more robust and user-friendly Docker deployment setup for BrainDB.

Key Changes

• Multi-stage Docker Build: Refactored the Dockerfile to use a multi-stage approach. This reduces the final image size and improves security by running the application as a non-root user (bun).
• Enhanced docker-compose.yml:
  • Added comprehensive environment variable mappings to allow easy configuration of LLM providers and security settings directly from a .env file.
  • Configured a named volume (braindb_data) to ensure SQLite database persistence across container restarts.
  • Added descriptive documentation comments for port and volume configurations.
• Improved Documentation: Updated the README.md with a detailed "Docker (recommended)" section that explains persistence, port mapping, and initial setup steps.

Verification

• Validated docker-compose.yml syntax using docker compose config.
• Verified that volume mounts and internal paths are correctly mapped for SQLite persistence.
• Confirmed the multi-stage build structure adheres to Bun's official deployment recommendations.

Fixes #4

[sakshar2303]

please review and merge .