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/ui-egui/src/menus.rs

@@ -484,6 +484,8 @@ fn file_dialog(app: &mut EffectcraftApp, id: &str, params: &Value) -> Option<Res
         "anim.applyPreset" => ("path", Ask::Open(&["ecpreset", "json"])),
         "view.exportGuides" => ("path", Ask::Save("Guides.json")),
         "view.importGuides" => ("path", Ask::Open(&["json"])),
+        "file.exportLottie" => ("path", Ask::Save("Animation.json")),
+        "file.importLottie" => ("path", Ask::Open(&["json", "lottie"])),
         "file.runScript" => ("path", Ask::Open(&["jsonl", "json", "txt"])),
         "file.replaceFootage" => ("path", Ask::Import),
         "file.collectFiles" => ("folder", Ask::Save("Collected Files")),