feat: direct playout mode, AEC far-end, audio processing switches

- Add --android/--direct-playout: bypass jitter buffer, decode on recv
  (matches Android engine architecture)
- Wire AEC far-end reference from decoded playout to encoder
- Add --no-aec, --no-agc, --no-fec, --no-silence, --no-denoise switches
- Fix BufferSize::Fixed(960) → Default for macOS CoreAudio compat
- Optimize wzp-codec, wzp-fec, audiopus, nnnoiseless in debug profile
- Add capture callback size diagnostic logging

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

Cargo.toml

@@ -53,3 +53,18 @@ wzp-fec = { path = "crates/wzp-fec" }
 wzp-crypto = { path = "crates/wzp-crypto" }
 wzp-transport = { path = "crates/wzp-transport" }
 wzp-client = { path = "crates/wzp-client" }
+
+# Optimize heavy compute deps even in debug builds —
+# real-time audio needs < 20ms per frame, impossible unoptimized.
+[profile.dev.package.nnnoiseless]
+opt-level = 3
+[profile.dev.package.audiopus_sys]
+opt-level = 3
+[profile.dev.package.audiopus]
+opt-level = 3
+[profile.dev.package.raptorq]
+opt-level = 3
+[profile.dev.package.wzp-codec]
+opt-level = 3
+[profile.dev.package.wzp-fec]
+opt-level = 3