Work through next priorities

[navitronic]

Summary

• add app flow coverage and stricter number-list validation
• improve empty states, mobile layout, keyboard focus styles, and Storybook coverage
• add CI, Node engine metadata, generated-output docs, and GitHub Pages deployment automation

Verification

• npm test
• npm run build
• npm run build-storybook
• npm audit --audit-level=moderate

Commits

• a3c1289: Add app flow tests
• b07cb0f: Validate number list inputs
• 7f94fb3: Show empty combination state
• 2d5237b: Improve mobile layout
• fe675f3: Add keyboard focus styling
• 25629f4: Expand Cage stories
• 8da4aa7: Add CI checks
• 77db732: Declare supported Node version
• 5231ded: Document generated outputs
• ab8f629: Automate GitHub Pages deployment