Foundations + themes — first 20 specs

Phase 1+2 of the Material.io parity programme (#049 audit): 20 foundational specs ratified. Foundations cluster covers elements, adaptive design, canonical layouts (Feed/List-detail/Supporting/Custom), UX writing, customization axes, selection states, interaction states (8 states + overlay opacity recipe), and window-size classes (Compact/Medium/Expanded/Large). Styles cluster covers colour roles (18 semantic roles), dynamic colour (HCT-based seed → 13-tone palette), customization levels, typography (15 type roles), shape (6-level radius scale), motion (5 duration + 5 easing tokens), and elevation (6 levels with shadow + tonal recipes).