Add Cesium debug mode to map config

[robyngit]

Add a debug option to the Cesium map configuration that enables built-in Cesium debugging layers and visual aids. This is useful for development and troubleshooting tiling, rendering, and camera behaviour.

When debug: true is set in the map config:

• Enable Cesium's tile coordinate imagery layer, Cesium.TileCoordinatesImageryProvider and Cesium.GridImageryProvider

Additional debug options

Consider enabling the following when debug mode is active:

• viewer.scene.globe._surface.tileProvider._debug.wireframe = true: Render terrain tiles in wireframe
• viewer.scene.debugShowFramesPerSecond = true: Display FPS counter
• viewer.scene.globe.showSkirts = false: Helps reveal tile edges more clearly
• Log information about the loaded layers
• Expose camera position in a small overlay

Debug will not automatically activate layer-level debugging properties, e.g. debugShowGeometricError in 3Dtiles, since these can already be activated by passing them into the cesiumOptions: {} property of the layer.