Frontend:
- two-sidebar layout (left: collapsible stats + visual controls; right:
navigation, edit, export) with a top-left Back button
- click-driven navigation via Set Start / Set Destination buttons
- graph edit toolkit (add and remove nodes and edges, with undo)
- floating zoom controls; floorplan overlay on by default with opacity slider
- nodes no longer draggable; smoother processing state when loading examples
Backend:
- force the Agg matplotlib backend and drop plt.show() so uploaded
(non-cached) images no longer crash the threaded pipeline
Deploy: floorplan rendered as DOM element, edges always visible
