feat: GPUI desktop port foundation

- scene crate: full project/scene/element model, serde round-trip
  proven against the web SerializedProject shape
- transfer crate: .ocp zip container, cross-compat with web fflate
  archives proven in both directions
- storage crate: filesystem project store replacing IndexedDB,
  .ocp import/export
- media crate: ffmpeg-next 8 decoder (frames, audio, thumbnails,
  waveform summaries)
- playback crate: wall-clock anchored, frame-rounded playback clock
- gpu crate: native texture readback; compositor renders headless
  offscreen on Vulkan (spike test)
- flake devshell: rust toolchain, GPUI native deps, ffmpeg dev,
  bindgen clang args; GPUI hello-world builds
- port plan in notes/gpui-port.md

1 files changed, 33 insertions, 0 deletions

diff --git a/rust/crates/commands/src/timeline/tracks_snapshot.rs b/rust/crates/commands/src/timeline/tracks_snapshot.rs
new file mode 100644
index 00000000..5108e123
--- /dev/null
+++ b/rust/crates/commands/src/timeline/tracks_snapshot.rs
@@ -0,0 +1,33 @@
+use scene::{Project, SceneTracks};
+
+use crate::command::{Command, CommandError, CommandResult};
+use crate::project_ext::active_scene_mut;
+
+pub struct TracksSnapshotCommand {
+    before: SceneTracks,
+    after: SceneTracks,
+}
+
+impl TracksSnapshotCommand {
+    pub fn new(before: SceneTracks, after: SceneTracks) -> Self {
+        Self { before, after }
+    }
+}
+
+impl Command for TracksSnapshotCommand {
+    fn execute(
+        &mut self,
+        project: &mut Project,
+    ) -> Result<Option<CommandResult>, CommandError> {
+        if let Some(scene) = active_scene_mut(project) {
+            scene.tracks = self.after.clone();
+        }
+        Ok(None)
+    }
+
+    fn undo(&mut self, project: &mut Project) {
+        if let Some(scene) = active_scene_mut(project) {
+            scene.tracks = self.before.clone();
+        }
+    }
+}