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/udf.rs

@@ -1250,8 +1250,10 @@ fn parse_udf_name(data: &[u8]) -> String {
     }
 }
 
-/// Merge overlapping or adjacent (start, count) ranges.
-fn merge_ranges(ranges: &[(u32, u32)]) -> Vec<(u32, u32)> {
+/// Merge overlapping or adjacent (start, count) ranges. Caller sorts by start
+/// first. Shared range utility — also used to build the disc's encrypted-content
+/// extent map (see `Disc::encrypted_content_ranges`).
+pub(crate) fn merge_ranges(ranges: &[(u32, u32)]) -> Vec<(u32, u32)> {
     if ranges.is_empty() {
         return Vec::new();
     }