[BUG] fix axis label overlap in plot_volume_source_estimates by using draw_idle()

[Famous077]

Fixed issue #13700

Problem

When plotting volume source estimates, axis labels were mangled and
overlapping on the colorbar and y-axis of the time series plot.
The MRI and colorbar also appeared shifted relative to the black background.

Root Cause

canvas.draw() was being called after each click/keypress event in
_press() and _onclick(), causing blitting artifacts when combined
with nilearn's plotting functions.

Fix

Replaced canvas.draw() with canvas.draw_idle() in both _press()
and _onclick() functions in mne/viz/_3d.py. This lets matplotlib
schedule the redraw properly and avoids the rendering artifacts.

Changes

• mne/viz/_3d.py: canvas.draw() → canvas.draw_idle() in _press() and _onclick()
• doc/changes/dev/13700.bugfix.rst: changelog entry
• doc/changes/names.inc: added contributor name

[Famous077]

All tests in mne/viz/tests/test_3d_mpl.py pass locally.
The 2 CI failures appear to be Azure Pipelines infrastructure
issues, unrelated to this change. Waiting for your review whenever you get a chance.