CLAP plugin hosting (isolated unsafe crate), stem bouncing

- soundcraft-clap-host: scans standard CLAP folders, loads plugins via
  clap-sys/libloading, implements the Plugin trait (audio, params, latency,
  notes); the only crate allowed unsafe, every block documented; stubs on wasm
- mixer, engine (mix.insert, engine.clap_plugins) and Mix window CLAP menu
- end-to-end tests against a Rust-built fixture plugin
- file.bounce_stems: one soloed file per track

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

Cargo.lock

@@ -623,6 +623,12 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "clap-sys"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a76abbdb2907f6fd97fb6bc0b7be96b77d328f2dd9669d1075cc03369ed22154"
+
 [[package]]
 name = "clipboard-win"
 version = "5.4.1"
@@ -3382,6 +3388,18 @@ dependencies = [
  "soundcraft-time",
 ]
 
+[[package]]
+name = "soundcraft-clap-host"
+version = "0.1.0"
+dependencies = [
+ "clap-sys",
+ "libloading",
+ "log",
+ "serde",
+ "soundcraft-dsp",
+ "thiserror 2.0.21",
+]
+
 [[package]]
 name = "soundcraft-cli"
 version = "0.1.0"
@@ -3413,6 +3431,7 @@ dependencies = [
  "serde",
  "serde_json",
  "soundcraft-audio-io",
+ "soundcraft-clap-host",
  "soundcraft-dsp",
  "soundcraft-midi",
  "soundcraft-mix",
@@ -3438,6 +3457,7 @@ dependencies = [
  "log",
  "rayon",
  "soundcraft-audio-io",
+ "soundcraft-clap-host",
  "soundcraft-dsp",
  "soundcraft-midi",
  "soundcraft-model",
@@ -3490,6 +3510,7 @@ dependencies = [
  "serde",
  "serde_json",
  "soundcraft-audio-io",
+ "soundcraft-clap-host",
  "soundcraft-dsp",
  "soundcraft-engine",
  "soundcraft-midi",