feat(motion): unify the animation selector to one `motion` prop — (a) of §D.12

`<Cascade>` was the last component using `animation` as its preset selector — a
vestige of the coordinated `cascade-*` system retired in Plan A. Every other
animatable component (Dialog, Popover, Drawer, …) already uses `motion`. Renames
`<Cascade>`'s prop + its context field `animation` → `motion`, so the framework
has ONE universal selector name (RFC §D.12 step a). `MotionPresetName` and the
low-level `data-animation-style` attr are unchanged.

- cascade: types `animation?` → `motion?`; context `CascadeContext.animation` →
  `.motion`; component destructure + getter; item reads `ctx?.motion`.
- docs/demo: README props table + usage, index usage, panel-cascade demo.

Verified at runtime: `<Cascade motion="scale-fade">` produces identical wiring —
items carry `data-animation-style="scale-fade"`, `animation-name: scale-in,
fade-in`, structural index 0/1/2/3. `check` clean for the touched files; no
dangling `animation`-prop reference remains (only the `data-animation-style` attr).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/uix/eidos/components/cascade/README.md

@@ -12,7 +12,7 @@ same foundation stagger do it (see "Two ways" below).
   let open = $state(true)
 </script>
 
-<Cascade {open} animation="scale-fade" style="display: grid; gap: 0.75rem; --motion-stagger-each: 60ms">
+<Cascade {open} motion="scale-fade" style="display: grid; gap: 0.75rem; --motion-stagger-each: 60ms">
   {#each items as item (item.id)}
     <Cascade.Item>{item.label}</Cascade.Item>
   {/each}
@@ -20,7 +20,7 @@ same foundation stagger do it (see "Two ways" below).
 ```
 
 `--motion-stagger-each: 0` (the default) → **parallel**; `N` → **cascade**. The keyframe,
-duration, easing and reduced-motion all come from the `animation` preset.
+duration, easing and reduced-motion all come from the `motion` preset.
 
 ## How it works — it reuses everything
 
@@ -45,7 +45,7 @@ down (`:nth-last-child`) so the last item leaves first.
 | Prop | Type | Default | Notes |
 | --- | --- | --- | --- |
 | `open` | `boolean` | `true` | Drives the staggered enter (forward) / exit (reverse) via `data-state`. |
-| `animation` | `MotionPresetName` | `'fade'` | The state-preset every item plays (`fade` / `scale-fade` / `slide-fade` / …). |
+| `motion` | `MotionPresetName` | `'fade'` | The state-preset every item plays (`fade` / `scale-fade` / `slide-fade` / …). Unified with the overlays' selector (RFC §D.12). |
 
 Plus any `HTMLAttributes<HTMLDivElement>`. Set the layout + the rhythm (`--motion-stagger-each`)
 here.

src/uix/eidos/components/cascade/cascade-item.svelte

@@ -30,7 +30,7 @@
 
 <div
 	data-cascade-item
-	data-animation-style={ctx?.animation ?? 'fade'}
+	data-animation-style={ctx?.motion ?? 'fade'}
 	data-state={ctx?.open ? 'open' : 'closed'}
 	out:leave
 	{...rest}

src/uix/eidos/components/cascade/cascade.svelte

@@ -17,14 +17,14 @@
 	import { setCascadeContext } from './context';
 	import type { CascadeProps } from './types';
 
-	let { open = true, animation = 'fade', children, ...rest }: CascadeProps = $props();
+	let { open = true, motion = 'fade', children, ...rest }: CascadeProps = $props();
 
 	setCascadeContext({
 		get open() {
 			return open;
 		},
-		get animation() {
-			return animation;
+		get motion() {
+			return motion;
 		}
 	});
 </script>

src/uix/eidos/components/cascade/context.ts

@@ -5,12 +5,13 @@ const KEY = Symbol('cascade');
 
 /**
  * What `<Cascade>` passes to its items: the container's open state + the state-preset the
- * items should play. Items read it to carry `data-state` + `data-animation-style` — they
- * never receive a timing or a visual var, only these two semantic/structural facts.
+ * items should play (the `motion` prop value). Items read it to carry `data-state` +
+ * `data-animation-style` — they never receive a timing or a visual var, only these two
+ * semantic/structural facts.
  */
 export type CascadeContext = {
 	readonly open: boolean;
-	readonly animation: MotionPresetName;
+	readonly motion: MotionPresetName;
 };
 
 export function setCascadeContext(ctx: CascadeContext): void {

src/uix/eidos/components/cascade/index.ts

@@ -2,7 +2,7 @@
 //
 //   import { Cascade } from '$uix/eidos/components/cascade';
 //
-//   <Cascade open={isOpen} animation="scale-fade" style="display: grid; gap: 0.75rem; --motion-stagger-each: 60ms">
+//   <Cascade open={isOpen} motion="scale-fade" style="display: grid; gap: 0.75rem; --motion-stagger-each: 60ms">
 //     {#each items as item (item.id)}
 //       <Cascade.Item>{item.label}</Cascade.Item>
 //     {/each}

src/uix/eidos/components/cascade/types.ts

@@ -13,9 +13,10 @@ export type CascadeProps = Omit<HTMLAttributes<HTMLDivElement>, 'children'> & {
 	/**
 	 * The state-preset every item plays (its `data-animation-style`) — any registered eidos
 	 * motion preset (`fade`, `scale-fade`, `slide-fade`, …). The keyframe / duration /
-	 * reduced-motion all come from the preset. @default 'fade'
+	 * reduced-motion all come from the preset. Unified with the overlays' selector: the
+	 * universal `motion` prop (RFC §D.12), not a separate `animation` axis. @default 'fade'
 	 */
-	animation?: MotionPresetName;
+	motion?: MotionPresetName;
 	children?: Snippet;
 };
 

web/routes/temas/animations/panel-cascade/+page.svelte

@@ -95,13 +95,13 @@
 	<p class="note">
 		Sin recipe propio: el contenedor se marca <code>data-stagger</code> (la foundation da el
 		índice por <code>:nth-child</code>), los items cargan un preset existente
-		(<code>animation="scale-fade"</code>) + <code>data-state</code>, y el stagger sale del
+		(<code>motion="scale-fade"</code>) + <code>data-state</code>, y el stagger sale del
 		preset (<code>--motion-stagger-each</code>, 0 = paralelo). Retención <code>out:</code> en el
 		item. Cero <code>--cascade-*</code>.
 	</p>
 	<Cascade
 		{open}
-		animation="scale-fade"
+		motion="scale-fade"
 		style="display: grid; grid-template-columns: repeat(auto-fill, minmax(11rem, 1fr)); gap: 0.75rem; padding: 1rem; border: 1px solid var(--color-border-subtle, #e5e5e5); border-radius: var(--radius-lg, 12px); min-block-size: 5rem; --motion-stagger-each: {rhythm}ms"
 	>
 		{#each cards as i (i)}