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, 4 insertions, 2 deletions

diff --git a/rust/crates/animation/src/bezier.rs b/rust/crates/animation/src/bezier.rs
index 6bec252f..bd433c47 100644
--- a/rust/crates/animation/src/bezier.rs
+++ b/rust/crates/animation/src/bezier.rs
@@ -140,17 +140,19 @@ mod tests {
     fn solve_progress_respects_flat_tangents() {
         let mut left = key(0, 0.0);
         left.right_handle = Some(CurveHandle {
-            dt: MediaTime::from_ticks(0),
+            dt: MediaTime::from_ticks(50),
             dv: 0.0,
         });
         let mut right = key(100, 100.0);
         right.left_handle = Some(CurveHandle {
-            dt: MediaTime::from_ticks(0),
+            dt: MediaTime::from_ticks(-50),
             dv: 0.0,
         });
         let early = solve_bezier_progress_for_time(MediaTime::from_ticks(25), &left, &right);
+        let mid = solve_bezier_progress_for_time(MediaTime::from_ticks(50), &left, &right);
         let late = solve_bezier_progress_for_time(MediaTime::from_ticks(75), &left, &right);
         assert!(early < 0.25);
+        assert!((mid - 0.5).abs() < 1e-3);
         assert!(late > 0.75);
     }
 }