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/specs/docker-deployment/spec.md

@@ -0,0 +1,42 @@
+## ADDED Requirements
+
+### Requirement: Docker image builds successfully
+The Docker image SHALL build without errors from the project root using `docker build`.
+
+#### Scenario: Build from project root
+- **WHEN** developer runs `docker build -t backup-tool .`
+- **THEN** the image builds successfully with all dependencies installed
+
+### Requirement: Docker Compose orchestrates full stack
+The `docker-compose.yml` SHALL start both backend and frontend services with a single command.
+
+#### Scenario: Start full stack
+- **WHEN** developer runs `docker compose up`
+- **THEN** backend API is accessible on port 8000
+- **AND** frontend is accessible on port 3000
+- **AND** services can communicate with each other
+
+### Requirement: Development mode supports hot reload
+The Docker setup SHALL support development mode with file watching and automatic reloading.
+
+#### Scenario: Backend code changes trigger reload
+- **WHEN** developer modifies a Python file in development mode
+- **THEN** the backend service restarts automatically
+- **AND** changes are reflected without manual container rebuild
+
+### Requirement: Production mode uses optimized build
+The production Docker setup SHALL use multi-stage builds and serve static files efficiently.
+
+#### Scenario: Production deployment
+- **WHEN** developer runs `docker compose -f docker-compose.yml up` in production configuration
+- **THEN** frontend assets are built and served by the backend
+- **AND** no development servers are running
+- **AND** image size is minimized
+
+### Requirement: Data persistence across restarts
+The Docker setup SHALL preserve SQLite database and backup files across container restarts.
+
+#### Scenario: Container restart preserves data
+- **WHEN** docker containers are stopped and restarted
+- **THEN** all existing backups and job history are preserved
+- **AND** no data loss occurs