[victorkemp]

A. MITC4+: support PSHELL MID4

• Parser: the bulk data reader rejected MID4 (error 1194). It now accepts it.
• Sign: SHELL_B was +T^2 [G4]. It is now -T^2 [G4], the Nastran convention, as in MYSTRAN_Documentation ABD_to_PSHELL (validated there against MSC and ComLab). WRITE_PCOMP_EQUIV already used it. With the old sign, MITC4+ reproduced the unsymmetric PCOMP only when G4 was negated.
• Other elements: a PSHELL MID4 on QUAD4 MIN4/MIN4T or TRIA3 now stops with new error 1966 ("only supported for CQUAD4 with QUAD4TYP MITC4+"). Those elements only add the coupling for an unsymmetric PCOMP, so before this MID4 would have been silently ignored.
• Force recovery: N = Ae + Bk and M = Be + Dk. A free coupled strip loaded at the reference plane reported M = Dk (My = -0.2) instead of 0. The same recovery feeds the MITC4+ buckling membrane forces.
• EBM (MATERIAL_PROPS_2D) is reset per element, and SHELL_BALP/TALP (PSHELL branch) are reset, so no values carry over from a previous element.

Tests:

• The closed-form coupled strip.
• An independent CLT PSHELL equivalent of an unsymmetric [0/45/-45/90] PCOMP at a 30 deg material angle. Every DOF matches the PCOMP.
• Coupled strip-column buckling, within 0.1% of exact.