gsp-phys: P6b wave 1 - shadow-forward guest CE copies to the physical engine

- the sema service captures the first eligible copy per push from the
  software resolver's own operands (the real push shape mixes guest RAM
  with emulated-VRAM shadow addresses, including physical destinations)
- HPA resolution: guest RAM through the shared guest-RAM file page cache,
  emulated VRAM through the mapping of its kernel shadow
- new scratch page-table pool: 16 zeroed page-table pages with their
  page-directory entries built before any engine access, handing out one
  whole 128-byte GMMU PTE fetch line per copy pair (16 PTEs, 512 pairs
  per boot, never reused; a PTE written into an already-fetched line is
  not observed and there is no invalidate path)
- the backend submits the copy on the module-owned channel and verifies
  the result host-side; every miss falls back to the ladder shadow copy,
  and the software pump remains authoritative
- live (full smoke, both parameters on): req=42 ok=42 verify_ok=42
  verify_fail=0 fallback=0, guest payload roundtrip ALL OK 64/64,
  clean latched release; defaults stay off

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