audit: cap the sparse-PTS reorder buffer, FMTS key state, zero KCD

Round-1 findings from the 10-phase release audit:

- SparsePtsReorder buffered its current GOP with no bound, draining only on
  a keyframe — an open-GOP or crafted program stream that never signals one
  could hold the whole title in RAM. Force-complete the GOP at
  MAX_GOP_FRAMES, matching the MPEG-2 parser's backstop.
- inject_unit_keys labelled a 2.1 FMTS disc as AACS 1.0 / bus-encryption
  off; FMTS is UHD-family, so synthesize the UHD version + bus encryption.
- The compiled Key Correction Data was a non-zero 16-byte constant fed into
  the Media Key derivation. Per the no-compiled-keys rule it is now all-zero;
  the chain still cannot complete on a real disc (documented), so this is
  behaviour-neutral — all variant tests pass unchanged.
- Fix stale doc references (broken `super::variants` intra-doc links, and
  `aacs::keys` comments) left by the module rename.

src/aacs/derive.rs

@@ -105,7 +105,7 @@ pub(crate) fn validate_processing_key(
     None
 }
 
-/// Compute v_mask from a UV value. [C] §3.2.3. Shared with [`super::variants`].
+/// Compute v_mask from a UV value. [C] §3.2.3. Shared with [`super::variant`].
 pub(super) fn calc_v_mask(uv: u32) -> u32 {
     let mut v_mask: u32 = 0xFFFF_FFFF;
     while (uv & !v_mask) == 0 && v_mask != 0 {
@@ -115,7 +115,7 @@ pub(super) fn calc_v_mask(uv: u32) -> u32 {
 }
 
 /// Derive processing key from device key using subset-difference tree traversal.
-/// [C] §3.2.4 (device-tree descent, MSB-branch, terminal PK). Shared with [`super::variants`].
+/// [C] §3.2.4 (device-tree descent, MSB-branch, terminal PK). Shared with [`super::variant`].
 pub(super) fn calc_pk_from_dk(
     dk: &[u8; 16],
     uv: u32,