Enable SBD GPU profile flow by default

[yoshifuminakamura]

Summary

• enable the SBD NSYS/NCU profile flow by default on supported NVIDIA GPU SBD systems
• keep the normal SBD FOM from the unprofiled run and allow explicit opt-out with BK_SBD_NCU_PROFILE=false or SBD_PROFILER_TOOL=none
• update the SBD profile shell test to cover default-on, explicit-off, and unsupported-system behavior

Tests

• bash -n programs/sbd/profile.sh programs/sbd/run.sh scripts/tests/test_sbd_ncu_profile.sh
• shellcheck -S error programs/sbd/profile.sh programs/sbd/run.sh scripts/tests/test_sbd_ncu_profile.sh
• bash scripts/tests/test_sbd_ncu_profile.sh
• bash scripts/tests/run_profile_data_shell_tests.sh all