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/m2ts.rs

@@ -3,9 +3,9 @@
 //! Write: prepends FMKV metadata header, then passes through BD-TS bytes.
 //! Read: extracts metadata header (or scans PMT), then yields BD-TS bytes.
 
-use std::io::{self, Read, Write, Seek, SeekFrom};
-use super::{IOStream, ReadSeek, meta, ts};
+use super::{meta, ts, IOStream, ReadSeek};
 use crate::disc::{DiscTitle, Stream as DiscStream};
+use std::io::{self, Read, Seek, SeekFrom, Write};
 
 /// Size of initial scan buffer for PMT/stream detection.
 const SCAN_SIZE: usize = 1024 * 1024;
@@ -54,7 +54,9 @@ impl M2tsStream {
         if let Ok(Some(m)) = meta::read_header(&mut reader) {
             return Ok(Self {
                 disc_title: m.to_title(),
-                mode: Mode::Read { reader: Box::new(reader) },
+                mode: Mode::Read {
+                    reader: Box::new(reader),
+                },
                 finished: false,
             });
         }
@@ -83,17 +85,23 @@ impl M2tsStream {
                 streams,
                 ..DiscTitle::empty()
             },
-            mode: Mode::Read { reader: Box::new(reader) },
+            mode: Mode::Read {
+                reader: Box::new(reader),
+            },
             finished: false,
         })
     }
 }
 
 impl IOStream for M2tsStream {
-    fn info(&self) -> &DiscTitle { &self.disc_title }
+    fn info(&self) -> &DiscTitle {
+        &self.disc_title
+    }
 
     fn finish(&mut self) -> io::Result<()> {
-        if self.finished { return Ok(()); }
+        if self.finished {
+            return Ok(());
+        }
         self.finished = true;
         if let Mode::Write { ref mut writer, .. } = self.mode {
             writer.flush()
@@ -106,7 +114,10 @@ impl IOStream for M2tsStream {
 impl Write for M2tsStream {
     fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
         match self.mode {
-            Mode::Write { ref mut writer, ref mut header_written } => {
+            Mode::Write {
+                ref mut writer,
+                ref mut header_written,
+            } => {
                 if !*header_written {
                     if !self.disc_title.streams.is_empty() {
                         let m = meta::M2tsMeta::from_title(&self.disc_title);
@@ -116,7 +127,10 @@ impl Write for M2tsStream {
                 }
                 writer.write(buf)
             }
-            Mode::Read { .. } => Err(io::Error::new(io::ErrorKind::Unsupported, "stream opened for reading")),
+            Mode::Read { .. } => Err(io::Error::new(
+                io::ErrorKind::Unsupported,
+                "stream opened for reading",
+            )),
         }
     }
 
@@ -133,7 +147,10 @@ impl Read for M2tsStream {
     fn read(&mut self, buf: &mut [u8]) -> io::Result<usize> {
         match self.mode {
             Mode::Read { ref mut reader } => reader.read(buf),
-            Mode::Write { .. } => Err(io::Error::new(io::ErrorKind::Unsupported, "stream opened for writing")),
+            Mode::Write { .. } => Err(io::Error::new(
+                io::ErrorKind::Unsupported,
+                "stream opened for writing",
+            )),
         }
     }
 }