Context passed to the *cngxDotStepperDot template. Drives the dot
body inside <cngx-dot-stepper>. The <span class="cngx-dot-stepper__dot">
shell - role="img", aria-current, aria-label, class
modifiers - stays library-owned; only the dot body content becomes
overrideable so consumers can swap the default empty body for an
icon, glyph, or branded indicator.
Smaller than CngxStepIndicatorContext on purpose - the dot
stepper does not surface step status/busy state visually, so the
context strips to the four fields a consumer actually needs.