Goal: Improve existing graph generation functionality, support static and real-time modes

Functional Requirements:

• Maintain existing static graph generation functionality (backward compatible)
• Add --live flag: display dataflow rates in real-time
• Add --output <file> to support multiple formats (PNG/SVG/DOT)
• Node status coloring (green=running, red=error, gray=stopped)

Technical Points:

• Use existing graphviz generation logic
• Real-time mode requires periodic coordinator queries to update graph
• Introduce colored or HTML color support

Acceptance Criteria:

$ dora graph my_dataflow --live --output graph.svg
# Generate SVG file showing real-time dataflow rates

Compatibility: Enhance existing command while maintaining backward compatibility