Remove _plan_mounts/_apply_mounts, _derived_position, CENTRELINE, hull_grid.cell_at,
mounted_position/mounted_cell and their tests (ruling remove-package-schematic-derivation).
Add Weapon makes a default-Position row; Mirror Mount mirrors each space within itself.
smoke_mounts rewritten (not run: bpy smokes are held off Starfire).
Co-Authored-By: Claude Sonnet 5.5 <noreply@anthropic.com>