blendertk v0.5.28

• 2026-07-26 — Encapsulated _mat_utils.py's 15 loose module-level helpers onto a _MatUtilsInternal base (mirror of mayatk); closes a blendertk-vs-mayatk divergence. MatUtils and MatUpdater now inherit _MatUtilsInternal (the gold-standard _<Class>Internal pattern), so _is_gp_material / _abspath / _principled_node / _resolve_images / … are @staticmethods reached as _MatUtilsInternal._x(...) rather than loose module functions. The cross-module importers (mat_manifest, render_opacity, scene_exporter/task_manager) and the texture_path_editor test were updated to match; module constants (SHADER_TEMPLATES, _PBR_DIRECT, …) stay module-level. No behavior change — private helpers only, no public-surface change beyond the two class base annotations. Verified in fresh Blender 5.1: test_texture_path_editor (13/13), test_render_opacity (26/26), test_scene_exporter, test_mat_anim_utils — all PASS.