Frames the view deterministically: Scene now carries padded per-axis bounds
(opstool's pad_ratio 0.15, with unit slack on degenerate axes) plus
axis_overrides() pinning range + autorange=False, so the model is never
flush against the viewport edge. Adds entity hover templates (Node #n /
Element #n with an empty extra tag), and an optional axis outline (grid +
ticks) - off by default so the SAP2000-like clean viewport is unchanged;
the coloured X/Y/Z axis lines always stay as the orientation cue.
The outline is exposed as a bool in the Plot Properties table, so the
table-driven dialog now builds a checkbox for kind=bool.
Colours that were hard-coded in the renderers now come from the shared
style: nodes, supports, nodal/element loads, section extrusions (+
opacity) and label font size. The PyVista frame LUT becomes a four-slot
palette [beam, truss, link, selected] with the cell scalar carrying the
family slot, so VTK matches the Plotly backend's per-family colouring
that landed earlier. Adds style helpers shared by both backends
(element_family_index, family_palette) and an immutable with_updates().
The style also gains the editable field table (STYLE_FIELDS) the Plot
Properties dialog is built from.
