Audit fixes + DVD support foundation (IFO, PS demux, MPEG-2, CSS crack)

Audit fixes (14 critical, 22 warnings):
- UDF: bounds checks on all ICB/FID parsing from disc data
- SCSI Linux: saturating_sub on residual, CDB length guard, buffer size guard
- SCSI macOS: SCSITaskStatus u32 (was u8 — stack corruption)
- AACS: EC mod_inv returns infinity instead of panic, key reduced mod n
- AACS: do_handshake tries all host certs (was returning on first failure)
- H.264: bounds check on SPS < 4 bytes
- ContentReader: error on missing unit key (was zero-fill)
- KEYDB: flat redirect loop (was recursive), 100MB response limit, Windows HOME fallback
- ISO writer: AVDP extent order, partition length, allocation cap
- Network: removed TCP_NODELAY on bulk stream
- MKV: guard on u64::MAX seek
- disc.rs: saturating_sub on extent offset, simplified dead region code
- cargo fmt (610 violations), cargo clippy --fix (55 auto-fixes)

DVD support (new files):
- src/ifo.rs — IFO parser (VIDEO_TS.IFO, VTS_XX_0.IFO, PGC chains, cells, streams) — 13 tests
- src/mux/ps.rs — MPEG-2 Program Stream demuxer (pack headers, PES, private stream 1) — 12 tests
- src/mux/codec/mpeg2.rs — MPEG-2 video parser (sequence headers, I-frame detection) — 15 tests
- src/css/crack.rs — split-attack algorithm (LFSR cipher needs verification — test ignored)

226 tests total (was 186), 1 ignored (CSS crack needs cipher verification).

tests/udf_tests.rs

@@ -1,9 +1,9 @@
 //! UDF parser tests using a MockSectorReader.
 
-use std::collections::HashMap;
 use libfreemkv::error::Result;
 use libfreemkv::sector::SectorReader;
 use libfreemkv::udf;
+use std::collections::HashMap;
 
 const SECTOR_SIZE: usize = 2048;
 
@@ -15,12 +15,18 @@ struct MockSectorReader {
 
 impl MockSectorReader {
     fn new() -> Self {
-        Self { sectors: HashMap::new() }
+        Self {
+            sectors: HashMap::new(),
+        }
     }
 
     /// Write a full 2048-byte sector at the given LBA.
     fn set_sector(&mut self, lba: u32, data: Vec<u8>) {
-        assert_eq!(data.len(), SECTOR_SIZE, "sector data must be exactly 2048 bytes");
+        assert_eq!(
+            data.len(),
+            SECTOR_SIZE,
+            "sector data must be exactly 2048 bytes"
+        );
         self.sectors.insert(lba, data);
     }
 
@@ -273,7 +279,10 @@ fn read_filesystem_no_partition_descriptor() {
     reader.set_sector(32, make_terminator());
 
     let result = udf::read_filesystem(&mut reader);
-    assert!(result.is_err(), "should fail when no partition descriptor in VDS");
+    assert!(
+        result.is_err(),
+        "should fail when no partition descriptor in VDS"
+    );
 }
 
 #[test]
@@ -425,7 +434,10 @@ fn find_dir_case_insensitive() {
 
     // PLAYLIST (empty)
     let playlist_data = make_parent_fid();
-    reader.set_sector(partition_start + 5, make_dir_icb(6, playlist_data.len() as u32));
+    reader.set_sector(
+        partition_start + 5,
+        make_dir_icb(6, playlist_data.len() as u32),
+    );
     reader.set_sector_partial(partition_start + 6, &playlist_data);
 
     let fs = udf::read_filesystem(&mut reader).expect("should parse");