Remove all 'Tour de Force' verbiage — rename to Demo everywhere

File rename: - tools/tour_de_force.py → tools/demo.py (git mv)

Internal changes in tools/demo.py: - Module docstring: "Tour de Force" → "Demo" - Class TourData → DemoData - Output file: tour_de_force.json → demo.json - Print messages: "Tour de Force" → "Demo" - argparse description updated

tools/render_html.py: - Docstring, TourData → DemoData, all json path references

CI (.github/workflows/pages.yml): - run: python tools/tour_de_force.py → python tools/demo.py

Docs: - docs/demo/demo-script.md: title + body references - docs/demo/demo-code.md: title "Tour de Force" removed - docs/demo/demo-midi.md: title "Music Plugin — Tour de Force" → "MIDI Plugin — Demo" - tools/README.md: section heading, file references, artifact table