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, 72 insertions, 0 deletions

diff --git a/rust/crates/graphics/src/params.rs b/rust/crates/graphics/src/params.rs
new file mode 100644
index 00000000..6c0fedd2
--- /dev/null
+++ b/rust/crates/graphics/src/params.rs
@@ -0,0 +1,72 @@
+use scene::params::{ParamValue, ParamValues};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub enum ParamGroup {
+    Stroke,
+}
+
+impl ParamGroup {
+    pub fn as_str(&self) -> &'static str {
+        match self {
+            ParamGroup::Stroke => "stroke",
+        }
+    }
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub struct SelectOption {
+    pub value: &'static str,
+    pub label: &'static str,
+}
+
+#[derive(Debug, Clone, PartialEq)]
+pub enum ParamDefinition {
+    Number {
+        key: &'static str,
+        label: &'static str,
+        group: Option<ParamGroup>,
+        default: f64,
+        min: f64,
+        max: Option<f64>,
+        step: f64,
+        short_label: Option<&'static str>,
+    },
+    Color {
+        key: &'static str,
+        label: &'static str,
+        group: Option<ParamGroup>,
+        default: &'static str,
+    },
+    Select {
+        key: &'static str,
+        label: &'static str,
+        group: Option<ParamGroup>,
+        default: &'static str,
+        options: &'static [SelectOption],
+    },
+}
+
+impl ParamDefinition {
+    pub fn key(&self) -> &'static str {
+        match self {
+            ParamDefinition::Number { key, .. } => key,
+            ParamDefinition::Color { key, .. } => key,
+            ParamDefinition::Select { key, .. } => key,
+        }
+    }
+
+    pub fn default_value(&self) -> ParamValue {
+        match self {
+            ParamDefinition::Number { default, .. } => ParamValue::Number(*default),
+            ParamDefinition::Color { default, .. } => ParamValue::String((*default).to_string()),
+            ParamDefinition::Select { default, .. } => ParamValue::String((*default).to_string()),
+        }
+    }
+}
+
+pub fn build_default_param_values(params: &[ParamDefinition]) -> ParamValues {
+    params
+        .iter()
+        .map(|param| (param.key().to_string(), param.default_value()))
+        .collect()
+}