perf(hub): fix iPhone instability and hero counter jank on clianything.cc

- Gate per-card backdrop-filter blur to desktop pointers; touch devices use
  the solid glass fallback (dozens of blur layers blew iOS Safari's GPU budget)
- Flatten card flip 3D contexts by default; enable per-card only on hover or
  during the flip transition
- Replace filter:blur(100px) ambient blobs with pre-softened gradients and
  hide the blend-mode grain overlay on touch devices
- Render decks once: fetch matrix registry with the other registries, defer
  the offscreen public deck + shelf, start counters after first paint
- Fix 627px-wide layout blowout on 390px phones (min-width guards on the
  empower and demo grids); let cards use the full phone width