Touch interaction model for coarse pointers, desktop unchanged

Gated on matchMedia("(hover: none)") so mouse/trackpad behavior is
untouched:
- Nav zones + edge markers only on the current tile; tapping any other
  tile selects it first. No more accidental traverses on touch.
- Edges always visible on touch (the hover glow becomes the tap
  affordance), glow while pressed via :active. Bands modestly shrunk so
  tile centers stay grab-to-pan.
- No hover ghost preview and no dropzones on touch (they were invisible
  tap traps without hover).
- Two-finger pinch to zoom (pointer-count based, works everywhere).
- Double-tap on empty space resets zoom, mirroring desktop dblclick.
- Kill iOS tap-highlight and long-press callout.

Adds /tmp/touchtest.mjs (15 checks) covering select/traverse/pinch/
double-tap/pan; domtest 52/52, exhaust 9/9, splash 6/6, fuzz clean.

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