Video track, Audio Unit hosting, plugin state and editors, Renderer and UI Customization

Video (new standalone crate soundcraft-video):
- Pure-Rust H.264 (Baseline/Main/High), ProRes (all flavours) and Motion JPEG decoding with
  ISO-BMFF demux, adapted from FilmCraft's crates; fuzzed with mutated/truncated movies
- TrackKind::Video with ClipContent::Video referencing Session.videos; file.import_video adds
  the picture track and the movie's audio; relinking on open; video.offset/online/list
- Video and Video Universe windows, thumbnails on the timeline, background decoding

Third-party plugins:
- Plugin state (CLAP state ext, VST3 component + controller state) saved in sessions
- Hosted instances created, state-loaded and dropped on the UI thread, never the audio thread
- Plugin editors: floating CLAP GUIs and VST3 views on macOS (verified with Melodyne)
- New isolated FFI crate soundcraft-au-host: Audio Units on macOS (effects and instruments,
  parameters, latency, MIDI, ClassInfo state), wired into the mixer and plugin browser

UI: Window > Renderer (speaker layout with live levels and object positions), Window > UI
Customization (interface scale, reduce motion), Window > Configurations > Auto-Update.

Fix: saturating sample-index math in clip rendering (hostile stretch values overflowed).

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

xtask/src/main.rs

@@ -21,9 +21,11 @@ const LAYERS: &[(&str, u8)] = &[
     ("time", 0),
     ("audio-io", 0),
     ("midi", 0),
+    ("video", 0),
     ("dsp", 1),
     ("clap-host", 1),
     ("vst3-host", 1),
+    ("au-host", 1),
     ("model", 2),
     ("mix", 3),
     ("engine", 4),
@@ -32,7 +34,7 @@ const LAYERS: &[(&str, u8)] = &[
     ("ui-egui", 6),
 ];
 /// Standalone format crates: no workspace dependencies at all (publishable on their own).
-const STANDALONE: &[&str] = &["time", "audio-io", "midi", "dsp"];
+const STANDALONE: &[&str] = &["time", "audio-io", "midi", "video", "dsp"];
 const UI_CRATES: &[&str] = &["egui", "eframe", "winit", "egui_kittest", "rfd", "egui-wgpu", "egui_glow"];
 const EXEMPT: &[&str] = &["soundcraft", "soundcraft-cli", "soundcraft-web", "xtask"];
 
@@ -119,6 +121,7 @@ const WASM: &[&str] = &[
     "soundcraft-time",
     "soundcraft-audio-io",
     "soundcraft-midi",
+    "soundcraft-video",
     "soundcraft-dsp",
     "soundcraft-model",
     "soundcraft-mix",