bc_x%ve3 never MPI-broadcast (duplicate ve2 in list)

[sbryngelson]

Bug

In `src/simulation/m_mpi_proxy.fpp`, the Fypp broadcast list at line 148 contains `bc_x%ve2` twice. The second occurrence should be `bc_x%ve3`. As a result, `bc_x%ve3` is never broadcast to non-root MPI ranks.

File: `src/simulation/m_mpi_proxy.fpp`, line 148

Impact: In multi-rank simulation runs using GRCBC boundary conditions, non-root ranks see uninitialized values for `bc_x%ve3`, producing incorrect boundary behavior.

Severity: Critical — silent data corruption on multi-rank runs with GRCBC boundaries.

[sbryngelson]

Fix: #1177