Add psychrometric chart to moist-air calculator

[iguchi-lab]

What changed

• port the equations and oblique h-x coordinate transform from iguchi-lab/psychrometric-chart to browser-native SVG
• draw dry-bulb, relative-humidity, humidity-ratio, and enthalpy lines at the selected pressure
• plot the current moist-air calculation as a red state point
• add responsive scrolling and SVG download
• document the source implementation
• add Node-based equation/rendering tests and GitHub Actions alongside the existing Python tests

Why

The moist-air calculator previously returned numerical properties only. Integrating the chart makes the calculated state easier to understand without adding a Matplotlib Lambda or another API request.

Validation

• automated chart equation and SVG-generation tests
• existing verified Python calculator test suite
• GitHub Actions runs both suites on this PR

Notes

The chart uses the water-surface Tetens equation across the displayed temperature range, matching the default behavior of iguchi-lab/psychrometric-chart.