GPU or CPU decided up front from the card's total memory, never from what is free

- Scaling: the 80%-of-card check runs right after the device ingest's sort and cut, where the
  observation and distinct-hkl counts are first known, instead of after the geometry smoothing;
  same counts, same decision, but a run that goes to the CPU no longer does the device smoothing
  (6.9 s on an 8 GB card for a 33 M observation set) or holds its memory meanwhile.
- Rigid body: engines budgeted on a quarter of the card's total (the validation's plan), not
  min(total/4, free - 1 GB). A busy card no longer sends the rigid body to the CPU (measured on an
  8 GB card: ~80 s and a different fit); engine allocations wait for GPU work beside the run, and
  an engine that cannot be set up fails the validation (RigidBodyGPUFailure) instead of falling
  back to the CPU.
- Beam-centre FFT: GPU when its footprint is at most half of the card's total, otherwise CPU,
  logged; no catch-and-rescore on the CPU after a GPU failure.
- FitPerFrameG reserves its per-frame vector (CPU scaling waited on the heap lock on Windows).
- get_gpu_free_memory(): cudaMemGetInfo, except on an integrated GPU under Linux, where free also
  counts MemAvailable less a tenth of the total. Used only where free memory is waited on
  (cuda_memory_available) or quoted in out-of-memory messages; it decides nothing.
  The two card-filling [CUDAMemHelpers] tests skip on integrated GPUs.
- Out-of-memory messages point at rugnux --no-gpu instead of "the CPU build".

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/ModelValidationTest.cpp

@@ -1182,18 +1182,11 @@ TEST_CASE("ModelValidation_RigidBodyTranslationDerivativeIsExact", "[ModelValida
 
 #ifdef JFJOCH_USE_CUDA
 namespace {
-    // A pool of `engines`, or a SKIP where there is none because the card is busy - over half its memory
-    // taken by something else, where the pool falls back to the CPU by design. Anywhere else no pool fails.
+    // A pool of `engines`: decided on the card's total memory, so there is one wherever there is a GPU.
     std::unique_ptr<RigidBodyGPUPool> TestPool(const gemmi::Model &model, const gemmi::UnitCell &cell,
                                                const gemmi::SpaceGroup &sg, double d_min, size_t observations,
                                                size_t engines, Logger &logger) {
         auto pool = RigidBodyGPUPool::Create(model, cell, sg, d_min, observations, engines, logger);
-        if (!pool) {
-            size_t free = 0, total = 0;
-            RigidBodyGPUEngine::MemoryInfo(free, total);
-            if (free < total / 2)
-                SKIP("No GPU engine: the card is busy (" << free / 1000000 << " of " << total / 1000000 << " MB free)");
-        }
         REQUIRE(pool);
         return pool;
     }