libfreemkv: rc.5.1 DVD correctness fixes

- CSS: unlock scrambled-sector reads on enforcing drives via bus-auth
  only; classify sense 6F/03 as CSS-locked; early-bail on a fully locked
  scan; gate the AACS handshake off DVD discs.
- DVD first-play menu no longer prepended to the feature: read the title
  VOBS base from vtstt_vobs (0xC4), not the menu VOBS vtsm_vobs (0xC0).
- Interlaced field-duration (DefaultDecodedFieldDuration) written as a
  direct TrackEntry child rather than inside Video, so Windows reports
  the correct frame rate.
- Audio channel count read from the AC-3 bitstream; FieldOrder set to
  TFF; per-track BPS tags.
- Structured disc diagnostics at --log-level 3; reduced per-operation
  log spam.

src/scsi/mod.rs

@@ -219,6 +219,16 @@ impl ScsiSense {
         self.sense_key == SENSE_KEY_ILLEGAL_REQUEST
     }
 
+    /// `true` for sense `05/6F/03` — MMC "READ OF SCRAMBLED SECTOR WITHOUT
+    /// AUTHENTICATION". The drive is enforcing CSS and the bus-auth read gate
+    /// is not (or no longer) open. Unlike a bare ILLEGAL REQUEST, this is
+    /// positive proof the sector is CSS-scrambled — the CSS crack scan keys on
+    /// it to distinguish "encrypted but locked" from "unreadable", and must
+    /// never collapse it to "unencrypted".
+    pub fn is_css_locked(&self) -> bool {
+        self.sense_key == SENSE_KEY_ILLEGAL_REQUEST && self.asc == 0x6F && self.ascq == 0x03
+    }
+
     /// `true` if `sense_key == ABORTED COMMAND (B)` — transient; one
     /// retry is usually safe.
     pub fn is_aborted_command(&self) -> bool {