BDN-Core-KS-01: Frozen Sector Selector for BDN Transfer Tests

This record freezes a conservative sector-level selector for the coefficient index k in future BDN transfer tests. It reduces manual freedom by using a finite fail-closed channel registry. It does not derive or validate any new physical constant and does not modify, retune, validate, or replace the frozen C106/v1.6 BDN-137 construction. It continues the BDN-TEP-01 transfer-extension priority record by defining a restricted k-selection infrastructure for future no-retuning tests. Corrected file package. Removed upload-facing metadata guidance from public files. No scientific content changes.