DVD vob_start absolute rebase + rc.5.3 audit fixes

- ifo.rs: rebase VTS title VOBS to absolute disc LBA (file_start_lba +
  vtstt_vobs); fixes DVD rips opening on the menu region instead of the
  movie (e.g. SOTL). Adds absolute-placement regression test.
- aacs/boil.rs: add mk_from_pk primitive (PK -> MK via MKB walk).
- dvdnav/: nav-VM command decoder + start-cell resolver seam, parked
  behind USE_NAV_RESOLVER (kept compiled, never executed).
- mux: FVI src.byte within-sector per spec; Unknown colour -> CICP
  unspecified (2,2,2,1); demux clear PCS -> NORMAL; ts.rs feed() base
  reset + boundary provenance fix.
- Assorted audit fixes (doc/comment/test accuracy) across the crate.

src/mux/videomap.rs

@@ -551,6 +551,21 @@ mod tests {
             },
             "measured CICP must override the coarse color_space enum"
         );
+
+        // Unknown colorimetry, SDR, no measured CICP → all code points map to
+        // "unspecified" (2), matching `from_color_space(Unknown)`. Both sinks of
+        // one title must emit 2, never 0.
+        let c = Colour::from_video(&mk(HdrFormat::Sdr, ColorSpace::Unknown, None));
+        assert_eq!(
+            c,
+            Colour {
+                primaries: 2,
+                transfer: 2,
+                matrix: 2,
+                full_range: false,
+            },
+            "Unknown colorimetry must emit CICP 'unspecified' (2), not 0"
+        );
     }
 
     #[test]