[magnesj]

History vectors (e.g. WOPTH) are identical in all realizations, so P10/P90 statistics make no sense. The ensemble curve set now plots only one realization for these vectors.

• The plotted realization is the first one that has a valid history vector, so a missing vector in realization 0 no longer gives an empty plot
• QC across all realizations: a warning is written to the Messages panel if some realizations are missing the vector, or have values that differ from the plotted one (compared per time step with a small relative tolerance)
• No statistics curves; the Statistics group is hidden
• Line thickness is configurable (default 3) instead of opacity
• Curve is plotted on top in z-order, also after highlighting is reset
• Clicking the curve does not select a realization

Fixes #15054

[magnesj]