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/disc_tests.rs

@@ -1,9 +1,9 @@
 //! Disc scanning pipeline tests.
 
-use std::collections::HashMap;
 use libfreemkv::error::Result;
 use libfreemkv::sector::SectorReader;
 use libfreemkv::{Disc, DiscTitle, ScanOptions};
+use std::collections::HashMap;
 
 const SECTOR_SIZE: usize = 2048;
 
@@ -14,7 +14,9 @@ struct MockSectorReader {
 
 impl MockSectorReader {
     fn new() -> Self {
-        Self { sectors: HashMap::new() }
+        Self {
+            sectors: HashMap::new(),
+        }
     }
 }
 
@@ -41,7 +43,10 @@ fn scan_image_empty_reader() {
     let mut reader = MockSectorReader::new();
     let opts = ScanOptions::default();
     let result = Disc::scan_image(&mut reader, 0, &opts);
-    assert!(result.is_err(), "scan_image should fail with empty reader (no AVDP)");
+    assert!(
+        result.is_err(),
+        "scan_image should fail with empty reader (no AVDP)"
+    );
 }
 
 // ── DiscTitle tests ────────────────────────────────────────────────────────
@@ -101,8 +106,14 @@ fn disc_title_total_sectors() {
     let mut t = DiscTitle::empty();
     assert_eq!(t.total_sectors(), 0);
 
-    t.extents.push(libfreemkv::Extent { start_lba: 0, sector_count: 100 });
-    t.extents.push(libfreemkv::Extent { start_lba: 200, sector_count: 50 });
+    t.extents.push(libfreemkv::Extent {
+        start_lba: 0,
+        sector_count: 100,
+    });
+    t.extents.push(libfreemkv::Extent {
+        start_lba: 200,
+        sector_count: 50,
+    });
     assert_eq!(t.total_sectors(), 150);
 }