M12.3: tracker core

New L2 crate effectcraft-track: per-point feature/search region tracking with
pyramid normalized cross-correlation and Lucas-Kanade (similarity + gain/bias)
sub-pixel refinement, confidence, adapt/stop/extrapolate/continue actions,
RGB/luminance/saturation channels, blur/enhance pre-processing, and
homography/affine/similarity solves.

Project: Motion Trackers > Tracker n > Track Point n property tree
(GroupKind::Tracker with type, target and options). Engine: track.* commands
(new/motion/stabilize/property/select/setType/setTarget/options/setPoint/
analyze/stop/apply/reset/delete/status), background or blocking analysis
job with progress and cancel (one undo step), apply to Transform, Stabilize
and Corner Pin. Renderer::layer_source for the tracker's frames.

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

xtask/src/main.rs

@@ -26,6 +26,7 @@ const LAYERS: &[(&str, u8)] = &[
     ("project", 2),
     ("text", 2),
     ("effects", 2),
+    ("track", 2),
     ("render", 3),
     ("media", 3),
     ("expr", 3),