- Introduce DrmScheme enum (Css/Aacs10/Aacs20/Aacs21) + drm module with
uniform detect/load dispatch across all four protection schemes.
- Land AACS 2.1 Media Key Variant framework in aacs::variants: chain
derivation, MKB record types 0x82/0x83, bit-0x02 SoftKCD and bit-0x04
online-challenge detection. Aacs21 dispatcher arm wired but commented
out pending validation against a Variant-scheme disc.
- Replace aacs2: bool with AacsVersion enum across ContentCertificate,
UnitKeyFile, ResolvedKeys. resolve_keys splits into _v1/_v2/_v21.
- Delete the libredrive raw-read VID shortcut from do_handshake; the
drive enforces the AGID requirement regardless of firmware-upload
state, so the shortcut spuriously dispatched E7017 instead of
surfacing the real downstream walls.