Lumina: map the axes + retire the static surface groups

Scope

• Map each data-elevation rung to a chrome bundle (fill / border / radius / shadow) via low-specificity attribute selectors — the rung's shadow is the rune surface's resting box-shadow depth, kept distinct from frame-shadow's per-guest drop-shadow (SPEC-107 §1); map each data-prominence value to a header type register (using the v0.22.0 type tokens).
• Set Lumina's per-rune defaultElevation / defaultProminence (and defaultWidth where a rune was a banner) so today's appearance is preserved: card-bucket runes → raised/flat, inline → flush, inset → sunken, banner → flush + width: full.
• Replace the four surfaces.css rune-name buckets (and the two nested :where(.rf-card, …) media-chrome lists) with [data-elevation] / [data-prominence] selectors.
• Seam with WORK-438: this produces the attribute-keyed surfaces.css (the content transform — rune-names → [data-elevation]). It does not introduce @layers; the skeleton/skin layering of that file belongs to the re-bucketing (WORK-438), which consumes this output. 425 hands 438 an already-attribute-keyed file.