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, 43 insertions, 0 deletions

diff --git a/rust/crates/timeline/src/placement/compatibility.rs b/rust/crates/timeline/src/placement/compatibility.rs
new file mode 100644
index 00000000..9512af49
--- /dev/null
+++ b/rust/crates/timeline/src/placement/compatibility.rs
@@ -0,0 +1,43 @@
+use crate::types::{ElementType, TrackType};
+
+pub fn get_track_type_for_element_type(element_type: ElementType) -> TrackType {
+    match element_type {
+        ElementType::Audio => TrackType::Audio,
+        ElementType::Text => TrackType::Text,
+        ElementType::Sticker | ElementType::Graphic => TrackType::Graphic,
+        ElementType::Effect => TrackType::Effect,
+        ElementType::Video | ElementType::Image => TrackType::Video,
+    }
+}
+
+pub fn can_element_go_on_track(element_type: ElementType, track_type: TrackType) -> bool {
+    get_track_type_for_element_type(element_type) == track_type
+}
+
+pub struct TrackCompatibility {
+    pub is_valid: bool,
+    pub error_message: Option<String>,
+}
+
+pub fn validate_element_track_compatibility(
+    element_type: ElementType,
+    track_type: TrackType,
+) -> TrackCompatibility {
+    let is_valid = can_element_go_on_track(element_type, track_type);
+
+    if !is_valid {
+        return TrackCompatibility {
+            is_valid: false,
+            error_message: Some(format!(
+                "{} elements cannot be placed on {} tracks",
+                element_type.as_str(),
+                track_type.as_str(),
+            )),
+        };
+    }
+
+    TrackCompatibility {
+        is_valid: true,
+        error_message: None,
+    }
+}