developer_panel: label each visualizer tab by its attribute

The tabbed multiparm now carries the sidefx::multi_label tag pointing at
attr#, so a tab reads "growth" or "dir" instead of "Vis 1", "Vis 2", and
the label travels with its instance when tabs are reordered. attr# defaults
to vis# (Houdini expands the # per instance) because an empty label draws
an unclickable sliver of a tab. No module code: the tag does the work.

Verified in a shadow Houdini 22.0.429 session: three instances show
growth / dir / vis3.

Co-Authored-By: Claude Fable 5.1 <[email protected]>

 otls/sop_lsgalante.developer_panel.1.0.hdalc | Bin 16908 -> 17269 bytes
 1 file changed, 0 insertions(+), 0 deletions(-)

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