Move codec_privates onto DiscTitle, eliminate duplicate methods

Design fix: codec_privates are now a field on DiscTitle, not a separate
parameter passed through the pipeline. This eliminates the root cause of
the network codec_private bug (forgot to pass the separate param).

API changes:
- output() takes (url, &DiscTitle) — no separate codec_privates param
- MkvOutputStream::create, M2tsOutputStream::create, NetworkOutputStream::connect
  all read codec_privates from title.codec_privates
- M2tsMeta::from_title() takes only &DiscTitle — reads privates from title
- Deleted from_title_with_privates (was the wrong-name duplicate)
- Merged read_header + read_header_from_stream into one read_header(impl Read)
- Deleted finish(self) from TsMuxer, keep only finish(&mut self)

Rule: ONE public method per action. No _with_X, _from_Y, _ref variants.

src/mux/network.rs

@@ -58,8 +58,8 @@ impl NetworkStream {
         stream.set_nodelay(true)?;
         let mut reader = BufReader::with_capacity(NET_BUF_SIZE, stream);
 
-        // Read FMKV metadata header (inline, since TcpStream doesn't impl Seek)
-        let disc_title = meta::read_header_from_stream(&mut reader)?
+        // Read FMKV metadata header
+        let disc_title = meta::read_header(&mut reader)?
             .ok_or_else(|| {
                 io::Error::new(
                     io::ErrorKind::InvalidData,
@@ -149,6 +149,7 @@ mod tests {
             chapters: Vec::new(),
             extents: Vec::new(),
             content_format: ContentFormat::BdTs,
+            codec_privates: Vec::new(),
         }
     }