Is your feature request related to a problem? Please describe.

The current version of Cartographer has no About dialog and no visible link to the documentation. In addition, Cartographer is deployed by different institutions and projects, each of which legally needs its own imprint; a hardcoded imprint would show
the wrong information for every deployment except one.

Describe the solution you'd like

Add two entries to the app footer:

• About — opens an About dialog containing a short description of the app, the version number, links to the source code and issue tracker, the imprint of the hosting institution, and the license.

• Docs — links to the documentation served under /docs of the current host.

Make the imprint in the About dialog configurable per deployment, following the same runtime-configuration pattern already used for the public path: values are passed as environment variables at docker run time (no rebuild needed)

All imprint variables are optional and independent; fields left unset are not displayed. If none is set, a built-in default imprint (ZenMEM / Paderborn University) is shown.