M11.4: Lottie export/import

New crate effectcraft-lottie (L3): export a comp to Lottie JSON / dotLottie
(precomp and base64 image assets; shape, solid, null, precomp, image and text
layers or glyph shapes; transforms with parenting, separated position,
anchor; keyframes with speed/influence converted to normalised i/o tangents,
hold keys, spatial ti/to; all shape items incl. gradients, dashes, trim,
repeater and path operators; masks, track mattes, blend modes, time remap,
timing, markers, optional expressions, a few Lottie effects) with a warnings
list for what Lottie cannot express, and the inverse import. Commands
file.exportLottie / file.importLottie with File > Export / Import entries.
Round-trip tests (values and rendered frames) and hand-written fixtures.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

crates/engine/src/commands/mod.rs

@@ -15,6 +15,7 @@ mod layer;
 mod layer_menu;
 mod layer_time;
 mod link;
+mod lottie;
 mod mask;
 mod prop;
 mod query;
@@ -100,6 +101,7 @@ pub fn command_specs() -> &'static [CommandSpec] {
         v.extend(animation::specs());
         v.extend(view::specs());
         v.extend(file_more::specs());
+        v.extend(lottie::specs());
         v.extend(comp_more::specs());
         v.extend(frontend::specs());
         v.extend(stubs::specs());