feat: add layer visibility toggle to map legend (#3303)

[pierreeurope]

Summary

Closes #3303 — Adds layer visibility toggle buttons to the map legend.

Problem

In read-only/exported maps, there was no way to toggle layer visibility since the side panel is not available. The legend showed layer names but no controls.

Solution

Added an eye icon toggle (EyeSeen/EyeUnseen) next to each layer name in the legend header. Clicking it toggles the layer's isVisible config via layerConfigChange.

Changes

• src/components/src/map/map-legend.tsx:
  • Added StyledLegendHeaderRow and StyledVisibilityToggle styled components
  • Extended LayerLegendHeaderFactory to accept onToggleLayerVisibility prop
  • Added eye icon toggle with visual feedback (opacity changes for hidden layers)
  • Added onToggleLayerVisibility to MapLegendProps and threaded it through
• src/components/src/map/map-legend-panel.tsx: Added onToggleLayerVisibility prop passthrough
• src/components/src/map/map-control.tsx: Added onToggleLayerVisibility to MapControlProps
• src/components/src/map-container.tsx: Added _handleToggleLayerVisibility handler that calls layerConfigChange

Behavior

• Eye icon appears next to each layer name in the legend
• Hidden layers show with reduced opacity and the EyeUnseen icon
• Toggle only appears when onToggleLayerVisibility is provided (backward compatible)