[FXC-5755] Fix case validation for user defined farfield auto symmetry plane

[sashok-flex]

Previous PR 1820 introduced a bug with case validation (see Cursor comment). In validation_simulation_params.py, _collect_asset_boundary_entities would only add "symmetric" boundary to a user-defined farfield when will_generate_forced_symmetry_plane() is True. This did not apply to the "auto" symmetry plane type. This PR changes the behavior to permit an "auto"-like symmetry plane to be detected.

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Note

Medium Risk
Touches boundary/ghost-surface validation logic that affects whether surfaces are considered present or deleted, which can change error vs warning behavior and BC completeness outcomes across farfield modes.

Overview
Fixes case validation so a UserDefinedFarfield can use an auto-detected symmetry plane (domain_type=None) when running with Geometry AI + beta mesher.

This extends symmetry-plane handling to treat user-defined farfields like auto for surface-deletion checks (via a new gai_and_beta_mesher flag) and ensures the symmetric ghost boundary is included in BC completeness checks for user-defined farfields under those conditions. Tests and surface-mesh fixtures are updated to cover the new path and to assert warnings are empty when valid.

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[benflexcompute]

Could you take a look at the AI comment?

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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