verify: post-read decrypt-verify gate + libaacs-strict verify + audit fixes

Post-read verify gate (new src/disc/verify.rs): UnitVerifier buffers/aligns the disc-absolute read stream into clip-file 6144-byte units, then makes one decryptability() decision per unit (CPI gate -> held keys -> key_fetch -> strict TS). POST_READ_VERIFY const kill-switch; fail-safe contract (only ever downgrades units it is confident are undecryptable; every doubt skips). Hooked into Disc::sweep (producer observes ciphertext -> WorkItem::MarkBad after the Good, FIFO-ordered) and Disc::patch (post-loop reverify_iso reads recovered units whole from the patched ISO). extract::clip_layouts enumerates AACS clips for the gate.

Standards-correct AACS verify: aacs::unit_is_clean_ts is a strict port of libaacs _verify_ts (all 32 TS syncs, not a majority vote); decrypt_unit accepts a key only on it; the majority verify_ts is removed. Deleted the Disc::verify_clips post-pass bolt-on (its primitive is absorbed by the read-path gate).

libaacs/DVD audit fixes: content-cert bus_encryption flag now read from bit 7 (was bit 0 - defeated the bus-key fail-loud gate); cc_id read from offset 14; title_cps_unit range-validated + 1->0 index-converted per libaacs. Corrected attack_crib ("functionally-equivalent" not "exact" port) and read_disc_key (READ DVD STRUCTURE 0xAD, not REPORT KEY) doc comments.

Also includes accumulated uncommitted work: key-fetch seam and TrueHD/DTS audio fix.

src/disc/sweep.rs

@@ -66,6 +66,14 @@ pub(super) enum WorkItem {
     /// tell them apart without parsing a flag.
     GapFill { pos: u64, len: u64 },
 
+    /// Post-read verify downgrade. The producer's `UnitVerifier` found that the
+    /// just-`Finished` clip unit at `[pos, pos+len)` is confidently undecryptable
+    /// (a silent bad read). The consumer re-records the range as `NonTrimmed` so
+    /// the patch pass re-reads it — the ISO bytes (ciphertext) already written by
+    /// the preceding `Good` are left in place for the patch to overwrite. FIFO
+    /// pipe ordering guarantees this arrives AFTER the `Good` that wrote them.
+    MarkBad { pos: u64, len: u64 },
+
     /// Producer wants the latest mapfile stats for the progress
     /// callback. Consumer responds on `prog_tx` with a fresh
     /// [`ProgressSnapshot`]. Best-effort: if the producer hasn't
@@ -174,6 +182,12 @@ impl Sink<WorkItem> for SweepSink {
                 }
                 self.map.record(pos, len, SectorStatus::NonTrimmed)?;
             }
+            WorkItem::MarkBad { pos, len } => {
+                // Verify downgrade: the ISO bytes are already written by the
+                // preceding Good; only the mapfile status changes so patch
+                // re-reads this range. No file write.
+                self.map.record(pos, len, SectorStatus::NonTrimmed)?;
+            }
             WorkItem::StatsRequest => {
                 let stats = self.map.stats();
                 let bad_ranges = self.map.ranges_with(&[