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>

common/CUDAWrapper.cpp

@@ -103,6 +103,10 @@ size_t get_gpu_total_memory(int32_t) {
     return 0;
 }
 
+bool get_gpu_free_memory(size_t &, size_t &) {
+    return false;
+}
+
 void set_gpu(int32_t dev_id) {}
 
 void pin_gpu() {}