Grid placement utilities: col/row-span, order, 7–12 columns, --sf-grid-N template vars

[jackgranatowski]

Problem

Grid support covers .sf-grid (auto), .sf-grid-cols-1..6 and a few uneven splits, but there are no placement utilities (column/row span, order, start/end) and no column templates beyond 6, nor --sf-grid-N template variables for variable-driven grids.

Scope

• .sf-col-span-* / .sf-row-span-*, .sf-order-first/-last, .sf-col-start/-end (opt-in utilities).
• .sf-grid-cols-7..12 and/or --sf-grid-cols-1..12 template tokens.
• Keep responsiveness container-query based, not viewport breakpoints (see repo out-of-scope stance on breakpoint utilities).
• Relates to the curated-utilities effort (Utilities: curated core set #248).

Acceptance

• Placement utilities emitted (opt-in)
• Columns 7–12 and/or template vars available
• Documented