feat: port domain crates to Rust (session 1 complete)

All green: cargo test --workspace (~300 tests, 0 failures).
- timeline (45): placement, resize/ripple, split, snap, retime,
  audio separation, scene helpers
- animation (73): bezier solver, channel sampling, keyframe ops,
  split/clamp/clone, param definitions
- commands (9): Command trait, BatchCommand, history, 19 concrete
  commands, freeze-frame port 1:1
- audio (22): audible collection, range mixing, mastering limiter,
  rms/peak buckets
- text (19): cosmic-text layout/measure/raster, backgrounds,
  decorations
- graphics (52): full CSS gradient parser, tiny-skia raster,
  4 shape definitions
- effect-defs (16): blur definition, registry, pass resolution
- mask-defs (19): all 9 mask renderers via tiny-skia
- renderer (6): node model + scene builder port
- desktop: GPUI projects screen wired to ProjectStore
- scene: factory (web defaults: v32, Main Track, 1920x1080, 30fps)

1 files changed, 105 insertions, 0 deletions

diff --git a/rust/crates/graphics/src/gradient/ast.rs b/rust/crates/graphics/src/gradient/ast.rs
new file mode 100644
index 00000000..d3336fea
--- /dev/null
+++ b/rust/crates/graphics/src/gradient/ast.rs
@@ -0,0 +1,105 @@
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum GradientKind {
+    Linear,
+    RepeatingLinear,
+    Radial,
+    RepeatingRadial,
+}
+
+impl GradientKind {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            GradientKind::Linear => "linear-gradient",
+            GradientKind::RepeatingLinear => "repeating-linear-gradient",
+            GradientKind::Radial => "radial-gradient",
+            GradientKind::RepeatingRadial => "repeating-radial-gradient",
+        }
+    }
+
+    pub fn is_linear(&self) -> bool {
+        matches!(self, GradientKind::Linear | GradientKind::RepeatingLinear)
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum LinearOrientation {
+    Directional(String),
+    Angular(String),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum Distance {
+    Percent(String),
+    PositionKeyword(String),
+    Calc(String),
+    Px(String),
+    Em(String),
+}
+
+#[derive(Debug, Clone, PartialEq, Default)]
+pub struct Position {
+    pub x: Option<Distance>,
+    pub y: Option<Distance>,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ShapeKind {
+    Circle,
+    Ellipse,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum ShapeStyle {
+    Distance(Distance),
+    ExtentKeyword(String),
+    Position(Position),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct Shape {
+    pub value: ShapeKind,
+    pub style: Option<ShapeStyle>,
+    pub at: Option<Position>,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum RadialOrientation {
+    Shape(Shape),
+    ExtentKeyword {
+        value: String,
+        at: Option<Position>,
+    },
+    DefaultRadial {
+        at: Position,
+    },
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum GradientOrientation {
+    Linear(LinearOrientation),
+    Radial(Vec<RadialOrientation>),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum Color {
+    Hex(String),
+    Literal(String),
+    Rgb(Vec<String>),
+    Rgba(Vec<String>),
+    Hsl([String; 3]),
+    Hsla([String; 4]),
+    Var(String),
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct ColorStop {
+    pub color: Color,
+    pub length: Option<Distance>,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct GradientAst {
+    pub kind: GradientKind,
+    pub orientation: Option<GradientOrientation>,
+    pub color_stops: Vec<ColorStop>,
+}