Replace text-only stance labels with SVG icons + tint shader per D-086.
Alpha-mask shader swaps color at runtime via ShaderMaterial parameter.
Icons: walk, crouch, careful, sprint at 18px inside ImplantPanel row.
Also fix stale UILayer/HUD test path in test_ui_framework_sprint15.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>