refactor(bbb): align pin_threads() comment with EEG/MRI sibling files

EEG and MRI both append "See src.core.determinism." to the §4-rule-3
comment block. BBB silently dropped the pointer in 4dab60f. This
restores cross-pipeline consistency.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/pipelines/bbb_pipeline.py

@@ -26,7 +26,7 @@ from src.core.storage import write_parquet
 logger = get_logger(__name__)
 
 # Pin BLAS / OpenMP / pyarrow to single-threaded mode so byte-determinism
-# (AGENTS.md §4 rule 3) holds across hardware.
+# (AGENTS.md §4 rule 3) holds across hardware. See src.core.determinism.
 pin_threads()
 
 # Suppress RDKit's noisy C++-level warning stream; we surface our own