brae v0.3.1

brae 0.3.1

The solver is unchanged from 0.3.0; this adds the command surface around it. The public GPU network is not open
yet, so brae node ships for review rather than use.

• brae benchmark — run a standard workload and compare machines. Every run writes brae-benchmark.json;
  there is no flag to remember.
• brae benchmark --list — samples are branches of
  simd-ai/brae-bench, pulled and cached on first use: 4 for timing,
  12 covering one brae capability each.
• brae node register | status | unregister — execs brae-agent, a separate binary linking neither CUDA
  nor the solver, so a machine keeps reporting when its brae build is broken.
• Samples containing codedFixedValue / codedMixed are refused: brae compiles those on the GPU, so a
  benchmark carrying code would run it on every machine that benchmarks.
• The transient solver refuses adjustTimeStep yes, an active MRFProperties, and any fvOptions file rather
  than marching without that physics.
• Unified-memory GPUs (GB10) now report their memory instead of appearing to have none.
• install.sh installs brae-agent when libcurl is present, and says so when it is not.

Upgrade with git pull && cmake --build build -j --target brae. 269 ctests on a GB10; sm_80/sm_90
compile-checked.