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/mkb.rs

@@ -68,7 +68,7 @@ pub fn walk_mkb(mkb: &[u8]) -> Vec<MkbRecord> {
 /// then the body — stopping at the `00 000000` end marker or a
 /// malformed/out-of-bounds length. Lazy (no body clone), so a find-one-record
 /// caller never materialises the multi-MB cvalue table. [`walk_mkb`] and every
-/// MKB record walk in `aacs::keys` are built on this, so the framing rules — and
+/// MKB record walk in `aacs::resolve`/`aacs::derive` are built on this, so the framing rules — and
 /// any future fix to them — live in exactly one place (they had drifted across
 /// six hand-rolled copies).
 pub(crate) fn mkb_records(mkb: &[u8]) -> impl Iterator<Item = (usize, u8, usize)> + '_ {