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).

src/mux/stdio.rs

@@ -1,8 +1,8 @@
 //! StdioStream — raw byte pipe via stdin/stdout. Format-agnostic.
 
-use std::io::{self, Read, Write};
 use super::IOStream;
 use crate::disc::DiscTitle;
+use std::io::{self, Read, Write};
 
 /// Stdio stream — reads from stdin, writes to stdout.
 ///
@@ -41,7 +41,9 @@ impl StdioStream {
 }
 
 impl IOStream for StdioStream {
-    fn info(&self) -> &DiscTitle { &self.disc_title }
+    fn info(&self) -> &DiscTitle {
+        &self.disc_title
+    }
     fn finish(&mut self) -> io::Result<()> {
         if let Some(ref mut w) = self.writer {
             w.flush()?;
@@ -54,8 +56,10 @@ impl Read for StdioStream {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         match self.reader {
             Some(ref mut r) => r.read(buf),
-            None => Err(io::Error::new(io::ErrorKind::Unsupported,
-                "stdio:// opened for output — cannot read")),
+            None => Err(io::Error::new(
+                io::ErrorKind::Unsupported,
+                "stdio:// opened for output — cannot read",
+            )),
         }
     }
 }
@@ -64,8 +68,10 @@ impl Write for StdioStream {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         match self.writer {
             Some(ref mut w) => w.write(buf),
-            None => Err(io::Error::new(io::ErrorKind::Unsupported,
-                "stdio:// opened for input — cannot write")),
+            None => Err(io::Error::new(
+                io::ErrorKind::Unsupported,
+                "stdio:// opened for input — cannot write",
+            )),
         }
     }
     fn flush(&mut self) -> io::Result<()> {