v0.10.1: Streams are PES, Disc::copy() for sector dumps, zero English

Architecture:
- One stream per format, bidirectional PES (read/write on same type)
- IsoStream merged into DiscStream (one type, any SectorReader)
- Disc::copy() for disc→ISO raw sector dump
- IOStream trait deleted, all byte-level Read/Write removed
- ContentReader/OpenDisc/open_title/open_input/open_output deleted
- CountingStream wrapper for progress tracking

Error codes:
- All io::Error English strings replaced with Error enum variants
- From<Error> for io::Error conversion
- Unused variants removed, new stream/mux variants added

Deleted: mkvout.rs, pesout.rs, isowriter.rs, mkv-muxer-plan.md
Updated: all docs, README stream table, CHANGELOG

238 tests, 0 clippy warnings.

docs/README.md

@@ -11,11 +11,12 @@ Technical documentation for [libfreemkv](https://github.com/freemkv/libfreemkv),
 | Document | What it covers |
 |----------|---------------|
 | [Architecture](architecture.md) | Module map, design principles, error codes, platform support |
-| [Drive Access](drive-access.md) | DriveSession, SCSI transport, profiles, unlock, why raw mode is needed |
+| [Drive Access](drive-access.md) | Drive, SCSI transport, profiles, unlock, why raw mode is needed |
 | [AACS Encryption](aacs.md) | Key resolution (4 paths), content decryption, bus encryption, SCSI handshake |
 | [UDF Filesystem](udf.md) | UDF 2.50 with metadata partitions, pointer chain, how files are read from disc |
 | [MPLS Playlists](mpls.md) | Playlist format, play items, STN stream table, coding types |
 | [CLPI Clip Info](clpi.md) | EP map (coarse + fine entries), timestamp-to-sector mapping, extent calculation |
+| [API Design](api-design.md) | Stream API design, PES pipeline, input/output resolution |
 
 ## Reading Order