Feature Request #553: add separate toggle for DE/DX markers in Map Layers

[echo-gravitas]

This PR implements Feature Request #553.

Previously, the DE and DX markers on the map could not be hidden independently. This change adds a dedicated DE/DX Markers option in Settings -> Map Layers.

What changed

• Added a new map-layer toggle: DE/DX Markers.
• The DE and DX markers in WorldMap are now rendered only when that option is enabled.
• The setting is persisted alongside the other map-layer preferences in openhamclock_mapLayers.
• The new option was integrated into the existing Map Overlays section in the Settings panel.
• The Map Overlays section was moved to the top of the layer list.
• Toggling now takes effect immediately without requiring a manual page reload.
• Also fixed an existing DX News Ticker issue:
  • disabling it hid it correctly,
  • but re-enabling it did not always show it again immediately.
  • Root cause was missing synchronization between the ticker's internal visibility state and updated mapLayers.
  • useMapLayers now dispatches a mapLayersChanged event so the ticker updates immediately in the same tab.

Note

I had to run npm i because package.json and package-lock.json were out of sync. The lockfile was updated accordingly.

[accius]

Nice PR — clean implementation, merging now. One fix I'm applying post-merge:

In src/components/SettingsPanel.jsx, the category rendering loop allows the overlay category to render when grouped['overlay'] is undefined (because hasBuiltInOverlays is true). The built-in overlay cards render fine, but then it hits:

grouped[key].forEach((layer) => {

This throws TypeError: Cannot read properties of undefined if no plugin layers have category: 'overlay' loaded (fresh install, plugin load failure, etc.). Fixed with:

(grouped[key] || []).forEach((layer) => {

Thanks for the contribution! 73