feat(codec): Phase 0 — swap audiopus → opusic-c + opusic-sys (libopus 1.5.2)

Phase 0 of the DRED integration (docs/PRD-dred-integration.md). No behavior
change: inband FEC stays ON, no DRED, same bitrate, same quality. This
commit unblocks Phase 1+ by getting us onto libopus 1.5.2 where DRED lives.

Rationale for going straight to a custom DecoderHandle: opusic-c::Decoder's
inner *mut OpusDecoder pointer is pub(crate), so we cannot reach it for the
Phase 3 DRED reconstruction path. Running two parallel decoders (one for
audio, one for DRED) would drift because the DRED decoder wouldn't see
normal decode calls. Single unified DecoderHandle over raw opusic-sys is
the only correct architecture, so we build it in Phase 0 rather than
rewriting opus_dec.rs twice.

Changes:
- Cargo.toml (workspace + wzp-codec): remove audiopus 0.3.0-rc.0, add
  opusic-c 1.5.5 (bundled + dred features), opusic-sys 0.6.0 (bundled),
  bytemuck 1. Pinned exactly for reproducible libopus 1.5.2.
- opus_enc.rs: rewritten against opusic_c::Encoder. Argument order for
  Encoder::new swapped (Channels first). set_inband_fec(bool) now maps
  to InbandFec::Mode1 (the libopus 1.5 equivalent of 1.3's LBRR). encode
  uses bytemuck::cast_slice<i16,u16> at the &[u16] boundary.
- dred_ffi.rs (new): DecoderHandle wrapping *mut OpusDecoder directly via
  opusic-sys. Owns the allocation, frees on Drop. Exposes decode,
  decode_lost, and a pub(crate) as_raw_ptr() for the future Phase 3 DRED
  reconstruction. Send+Sync justified via &mut self access discipline.
- opus_dec.rs: rewritten as a thin AudioDecoder impl over DecoderHandle.
  Behavior identical to pre-swap.

Verification (Phase 0 acceptance gates):
- cargo check --workspace: clean (30 pre-existing warnings in jni_bridge.rs
  unrelated to this work; zero in changed files).
- cargo test -p wzp-codec: 53 tests pass (50 pre-swap + 6 new: 3 in
  dred_ffi.rs for DecoderHandle lifecycle, 3 in opus_enc.rs for version
  check and roundtrip).
- linked_libopus_is_1_5 test asserts opusic_c::version() contains "1.5" —
  hard signal that the swap landed correctly.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Cargo.lock

@@ -119,26 +119,6 @@ dependencies = [
  "winapi",
 ]
 
-[[package]]
-name = "audiopus"
-version = "0.3.0-rc.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ab55eb0e56d7c6de3d59f544e5db122d7725ec33be6a276ee8241f3be6473955"
-dependencies = [
- "audiopus_sys",
-]
-
-[[package]]
-name = "audiopus_sys"
-version = "0.2.2"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "62314a1546a2064e033665d658e88c620a62904be945f8147e6b16c3db9f8651"
-dependencies = [
- "cmake",
- "log",
- "pkg-config",
-]
-
 [[package]]
 name = "autocfg"
 version = "1.5.0"
@@ -389,6 +369,12 @@ version = "3.20.2"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "5d20789868f4b01b2f2caec9f5c4e0213b41e3e5702a50157d699ae31ced2fcb"
 
+[[package]]
+name = "bytemuck"
+version = "1.25.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "c8efb64bd706a16a1bdde310ae86b351e4d21550d98d056f22f8a7f7a2183fec"
+
 [[package]]
 name = "byteorder"
 version = "1.5.0"
@@ -2125,6 +2111,24 @@ version = "0.2.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "04744f49eae99ab78e0d5c0b603ab218f515ea8cfe5a456d7629ad883a3b6e7d"
 
+[[package]]
+name = "opusic-c"
+version = "1.5.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "9486eb5a1a735bf56430b5b44e21157be30ac9fcc17999ba309981b8bd90d2ff"
+dependencies = [
+ "opusic-sys",
+]
+
+[[package]]
+name = "opusic-sys"
+version = "0.6.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "dc3280fe5b6f97ac1a35a0ac003e2fb0b92f8e4bdf2b2057e1bf9b87acca5696"
+dependencies = [
+ "cmake",
+]
+
 [[package]]
 name = "os_str_bytes"
 version = "6.6.1"
@@ -4309,9 +4313,11 @@ dependencies = [
 name = "wzp-codec"
 version = "0.1.0"
 dependencies = [
- "audiopus",
+ "bytemuck",
  "codec2",
  "nnnoiseless",
+ "opusic-c",
+ "opusic-sys",
  "rand 0.8.5",
  "tracing",
  "wzp-proto",