mux: wire TrueHD channel probe into iso:// mux setup

correct_truehd_channels() probes the first DECRYPTED access units of the
chosen title (TrueHD PIDs, bounded 8 MiB read of the first extent) and
sets AudioStream.channels from the MLP major sync — fixing the MPLS
audio_format understatement (5.1 declared on a 7.1/Atmos TrueHD track).
Regenerates the basic codec label for the corrected count; richer
editorial labels are left untouched. Wired in resolve.rs input() for
iso:// after decrypt_with (the m2ts is only decryptable post-key), using
a fresh reader so the mux reader is undisturbed. generate_audio_label
made pub(crate).

src/mux/resolve.rs

@@ -216,8 +216,15 @@ pub fn input(url: &str, opts: &InputOptions) -> io::Result<Box<dyn crate::pes::S
                 }
                 .into());
             }
-            let title = disc.titles[idx].clone();
+            // Correct TrueHD channel counts (MPLS understates 7.1/Atmos as 5.1)
+            // by probing the first DECRYPTED access units of the chosen title.
+            // A fresh reader avoids disturbing the mux reader below.
             let keys = disc.decrypt_keys();
+            if let Ok(probe) = crate::io::file_sector_source::FileSectorSource::open(path) {
+                let mut dec = crate::sector::DecryptingSectorSource::new(probe, keys.clone());
+                crate::disc::correct_truehd_channels(&mut dec, &mut disc.titles[idx]);
+            }
+            let title = disc.titles[idx].clone();
             let format = disc.content_format;
             // ISO file: 16 MiB batch — sequential read from fast
             // storage, no bad sectors. Measured optimum on the rip1