## Why

The current backup tool uses a simple `requirements.txt` for dependency management and lacks containerization. This makes deployment inconsistent across environments and complicates dependency resolution. Converting to a proper `pyproject.toml` setup and adding Docker support will provide reproducible builds, standardized packaging, and one-command deployment for users.

## What Changes

- **Convert backend to pyproject.toml**: Replace `requirements.txt` with a modern `pyproject.toml` including project metadata, dependencies, build system, and optional dev/test dependencies
- **Add Dockerfile**: Multi-stage Docker build for the Python backend with proper layer caching
- **Add docker-compose.yml**: Orchestrate backend + frontend services with volume mounts and environment configuration
- **Add .dockerignore**: Optimize build context and exclude unnecessary files
- **Update README**: Add Docker deployment instructions
- **Frontend containerization (optional)**: Dockerfile for production frontend build served via nginx or integrated into backend static serving

## Capabilities

### New Capabilities
- `docker-deployment`: Container-based deployment with Docker and docker-compose for consistent environments
- `python-packaging`: Modern Python packaging with pyproject.toml, proper dependency groups, and build tooling

### Modified Capabilities
- None (this is a build/deployment improvement, no spec-level behavior changes)

## Impact

- **Build system**: Replaces `requirements.txt` with `pyproject.toml` (standard modern Python practice)
- **Deployment**: New Docker-based deployment path alongside existing manual setup
- **CI/CD**: Enables standardized container builds for CI pipelines
- **Developer experience**: `docker compose up` to start full stack instead of manual venv + npm setup
- **No API changes**: All existing endpoints and functionality remain unchanged