T6.1: AV1 encoder/decoder with HW probe + SVT-AV1 SW fallback

- New: av1_obu.rs — OBU framer, depacketizer, keyframe detection, LEB128 helpers
- New: dav1d.rs — SW AV1 decoder wrapper (shiguredo_dav1d)
- New: svt_av1.rs — SW AV1 encoder wrapper (shiguredo_svt_av1)
- Add CodecId::Av1Main = 12 with match-arm fixes in downstream crates
- Add VideoToolboxAv1Decoder for macOS M3+ HW decode
- Add MediaCodecAv1Encoder/Decoder for Android (video/av01)
- Add extract_sequence_header_obu() helper for AV1 decoder CSD
- Add 10-frame encode-decode roundtrip test (svt_av1 + dav1d)
- Fix clippy unused import in dav1d.rs
- 15 tests; all workspace tests pass; cargo fmt clean

crates/wzp-video/src/lib.rs

@@ -4,7 +4,9 @@
 //! packetization (NAL fragmentation / reassembly).  Platform encoders and
 //! decoders land in T4.2/T4.3/T5.4.
 
+pub mod av1_obu;
 pub mod controller;
+pub mod dav1d;
 pub mod decoder;
 pub mod depacketizer;
 pub mod encoder;
@@ -13,19 +15,24 @@ pub mod framer;
 pub mod mediacodec;
 pub mod nack;
 pub mod simulcast;
+pub mod svt_av1;
 pub mod videotoolbox;
 
+pub use av1_obu::{Av1Depacketizer, Av1ObuFramer, is_keyframe_obu};
 pub use controller::{VideoQualityController, VideoTarget};
+pub use dav1d::Dav1dDecoder;
 pub use decoder::VideoDecoder;
 pub use depacketizer::H264Depacketizer;
 pub use encoder::{VideoEncoder, VideoError, VideoFrame};
 pub use encoder_mode::EncoderMode;
 pub use framer::{FramedPacket, H264Framer};
 pub use mediacodec::{
-    MediaCodecDecoder, MediaCodecEncoder, MediaCodecHevcDecoder, MediaCodecHevcEncoder,
+    MediaCodecAv1Decoder, MediaCodecAv1Encoder, MediaCodecDecoder, MediaCodecEncoder,
+    MediaCodecHevcDecoder, MediaCodecHevcEncoder,
 };
 pub use nack::{CachedPacket, NackAction, NackReceiver, NackSender};
 pub use simulcast::{LayerPacket, LayerTarget, SimulcastEncoder, SimulcastLayer};
+pub use svt_av1::SvtAv1Encoder;
 pub use videotoolbox::{
     VideoToolboxDecoder, VideoToolboxEncoder, VideoToolboxHevcDecoder, VideoToolboxHevcEncoder,
 };