File headers: use SPDX license identifiers

add_mesh_discombobulator/mesh_discombobulator.py

add_mesh_extra_objects/add_mesh_teapot.py

amaranth/render/meshlight_add.py

btrace/bTrace_panel.py

curve_assign_shapekey.py

curve_tools/curves.py

curve_tools/operators.py

greasepencil_tools/import_brush_pack.py

greasepencil_tools/rotate_canvas.py

io_export_paper_model.py

lighting_tri_lights.py

magic_uv/lib/bglx.py

materials_utils/enum_values.py

materials_utils/functions.py

materials_utils/menus.py

materials_utils/operators.py

materials_utils/preferences.py

mesh_auto_mirror.py

object_carver/carver_draw.py

object_carver/carver_operator.py