Relocate the shared low-level primitives into a single crypto module: aes_ecb_encrypt/decrypt, aes_cbc_decrypt, aes_g (from content/variant) and aesg3 + AESG3_SEED (from keys), plus AACS_IV. Fixes the scatter where AES-G lived in the 2.1 file and AES-G3 in keys. Relocation only — no rename, no logic change (logic-hash identical to baseline; 277 items; 2210 tests green).