Add IOStream trait and stream-based I/O architecture

Introduce IOStream trait for uniform read/write across disc, file,
network, and null streams. Rename Title→DiscTitle, add stream URL
resolver, split old stream.rs into focused modules (m2ts, mkvstream,
network, disc, null, resolve, meta).

src/mux/mod.rs

@@ -1,25 +1,60 @@
-//! MKV muxing pipeline.
+//! Stream-based I/O pipeline.
 //!
-//! Provides BD transport stream → MKV remuxing via composable streams.
-//!
-//! The main type is `MkvStream` — wraps any `Write + Seek` output,
-//! receives raw BD-TS bytes via `write()`, outputs MKV.
+//! All formats are streams. Two URLs, left reads, right writes:
 //!
 //! ```text
-//! disc.rip(title, MkvStream::new(file, &title))
+//! freemkv disc:// mkv://Dune.mkv
+//! freemkv m2ts://Dune.m2ts mkv://Dune.mkv
+//! freemkv disc:// network://10.0.0.1:9000
 //! ```
 //!
-//! Components (for advanced use):
-//! - `ts`: BD transport stream demuxer (192-byte packets → PES frames)
-//! - `ebml`: EBML write primitives for Matroska container
-//! - `mkv`: MKV muxer (tracks, clusters, blocks, cues)
-//! - `codec`: Elementary stream parsers (frame boundaries, codec headers)
+//! Streams implement `IOStream` for uniform handling:
+//!
+//! ```text
+//! let mut input = open_input("disc://", &opts)?;
+//! let mut output = open_output("mkv://Dune.mkv", input.info())?;
+//! io::copy(&mut *input, &mut *output)?;
+//! output.finish()?;
+//! ```
 
 pub mod ebml;
 pub mod ts;
 pub mod mkv;
 pub mod codec;
 pub mod lookahead;
-pub mod stream;
+pub mod meta;
+mod m2ts;
+mod mkvstream;
+pub mod network;
+pub mod disc;
+pub mod null;
+pub mod resolve;
 
-pub use stream::MkvStream;
+pub use m2ts::M2tsStream;
+pub use mkvstream::MkvStream;
+pub use network::NetworkStream;
+pub use disc::{DiscStream, DiscOptions};
+pub use null::NullStream;
+pub use resolve::{open_input, open_output, parse_url, InputOptions, StreamUrl};
+
+use std::io::{self, Read, Write, Seek};
+use crate::disc::DiscTitle;
+
+/// Common interface for all stream types.
+///
+/// A stream can be opened for reading or created for writing.
+/// Calling the unsupported direction returns an error.
+pub trait IOStream: Read + Write {
+    /// Get stream metadata.
+    fn info(&self) -> &DiscTitle;
+
+    /// Finalize the stream (flush, write index/cues, close).
+    fn finish(&mut self) -> io::Result<()>;
+}
+
+// Combined traits for internal trait objects.
+pub(crate) trait ReadSeek: Read + Seek {}
+impl<T: Read + Seek> ReadSeek for T {}
+
+pub(crate) trait WriteSeek: Write + Seek {}
+impl<T: Write + Seek> WriteSeek for T {}