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, 46 insertions, 0 deletions

diff --git a/rust/crates/commands/src/command.rs b/rust/crates/commands/src/command.rs
new file mode 100644
index 00000000..c13468e7
--- /dev/null
+++ b/rust/crates/commands/src/command.rs
@@ -0,0 +1,46 @@
+use scene::{ElementRef, Project};
+use thiserror::Error;
+
+#[derive(Debug, Error)]
+pub enum CommandError {
+    #[error("source track or element not found")]
+    SourceNotFound,
+    #[error("target track not found")]
+    TargetTrackNotFound,
+    #[error("{0}")]
+    IncompatiblePlacement(String),
+}
+
+#[derive(Clone, Debug, Default, PartialEq)]
+pub struct SelectionPatch {
+    pub selected_elements: Vec<ElementRef>,
+}
+
+#[derive(Clone, Debug, Default, PartialEq)]
+pub struct CommandResult {
+    pub selection: Option<SelectionPatch>,
+}
+
+impl CommandResult {
+    pub fn element_selection(selected_elements: Vec<ElementRef>) -> Self {
+        Self {
+            selection: Some(SelectionPatch { selected_elements }),
+        }
+    }
+}
+
+pub trait Command {
+    fn execute(
+        &mut self,
+        project: &mut Project,
+    ) -> Result<Option<CommandResult>, CommandError>;
+
+    fn undo(&mut self, project: &mut Project);
+
+    fn redo(
+        &mut self,
+        project: &mut Project,
+    ) -> Result<Option<CommandResult>, CommandError> {
+        self.execute(project)
+    }
+}