Add color scheme selector (palette presets) to generated HTML

[aplgr]

Goal

Add optional color schemes for the GroveGrid visualization (palette presets), selectable in the generated HTML.

Why

Different lighting/printing contexts benefit from different palettes (e.g. colorblind-friendly, high-contrast).

Scope

• Add a small UI control (dropdown or segmented buttons): Default, High contrast, Colorblind-friendly (names can be adjusted).
• Switching the palette updates the chart without regenerating the HTML.
• Persist the chosen palette in localStorage so reload keeps it.

Acceptance criteria

• UI control exists and is unobtrusive.
• Changing it updates the chart immediately.
• Choice persists across reloads.
• Default behavior stays unchanged when no selection is made.

Notes / hints

• Keep it self-contained (no external deps).
• If palette wiring touches ECharts config: prefer a small mapping object like palettes = { default: {...}, highContrast: {...} }.