Review of the map feature

- [x] When switching to dark mode the map is full white. It can be cool to have a default map style for dark mode
=> just remove the background color on the style and iy's OK. BTW, we can define the background color in gephi, so we need to remove it. Also, having two default map styles (light and dark) is mandatory. (major).

- [x] There is no indication on which attributs the geo coordinates are taken. We must add an explanation in the application and say to the end user that he must apply a geospatial layout before to display the map background. Don't know if it's here or on the geo layout page. (major)

- [x] When you open a not geographical graph like "Les misérables" and then you apply the map layer, you can zoom in, but you can't zoom out. I know it's due to the min map zoom, , but when you have bad coordinate, it's really annoying. (minor)

- [x] Map layout on metro gexf (check [here](https://github.com/totetmatt/gexf/tree/master/metro)) is not working( before to apply geospatial layout) (critical)

- [x] Open the metro graph of Paris, (node size 0.002, edge size : 0.001), and zoom on it. Then change the map style by [this one](https://tiles.openfreemap.org/styles/bright) => Nodes position are wrong, the map is reset to see the whole planet. (major)

- [x] Node & edge size are weird in geo: when you open the Paris RER graph, apply the geographical layout and see the result. (minor)

No files, tests, or entry points are named. Start by reproducing the six listed map scenarios, including dark mode, the metro graph, zooming, style changes, and node or edge sizing, then trace the map feature implementation. Done means each checked behavior is verified without regressions and the coordinate explanation is present in the appropriate application area.

Written by the indexing model from the issue text.