feat: dockerize app and convert to pyproject setup

- Add pyproject.toml with proper metadata and dependency groups
- Create multi-stage Dockerfile for backend
- Add docker-compose.yml with dev/prod profiles
- Create frontend Dockerfile with nginx
- Add .dockerignore for optimized builds
- Update README with Docker instructions and troubleshooting
- Remove requirements.txt in favor of pyproject.toml
- Ensure data persistence with Docker volumes

openspec/changes/dockerize-and-pyproject-setup/proposal.md

@@ -0,0 +1,29 @@
+## 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