v0.13.0

Export the current TUI plot as a real PNG -- press p while a plot is showing. The image is self-documenting (node name as the title, a footer naming the source file and the same sampling note shown in the detail panel) and saved to the current directory as <source-file-stem>_<node-name>.png, overwritten on repeat presses.

Uses matplotlib, an optional extra (pip install 'rootfileviewer[matplotlib]' or [all]) following the same lean-by-default pattern as pyarrow/h5py/pandas -- without it, p shows a toast explaining how to install it rather than crashing. If a logarithmic x/y axis is toggled (x/y) when you press p, the PNG reflects that too, using matplotlib's own native log-scale axes.