the layout graph is maintained, and the shine draws for real

- the interface's layout graph is maintained as anchors change instead of rediscovered from scratch: 1.48 ms per mutated frame becomes 34 µs, and end to end a running cast now costs +0.14 ms where it cost +4.33
- the autocast shine draws its authored population — 1200 particles through the star's own projection, spinning as the model says
- the shine is clipped to its own widget: the model frame installs its rect as the viewport, so nothing it draws leaves the button

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

crates/benilla-ui/src/script/object.rs

@@ -30,7 +30,7 @@ mod frame_state;
 mod layout_methods;
 pub(crate) mod movable;
 pub(crate) mod toplevel;
-pub(crate) use layout_methods::anchor_bits_eq;
+pub(crate) use layout_methods::{anchor_bits_eq, anchor_retarget_is_structural};
 pub(crate) use movable::{advance_move, advance_size, FrameMove, FrameSizing};
 
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