feat(dropdown-menu): adopt the `overlay` elevation plane (B2)

Content / SubContent now carry `data-depth="overlay"` and take their
surface · border · shadow · halo from the overlay plane instead of the
recipe. Prune the now-redundant recipe tokens (content-border-width /
border-color / bg / shadow) — the plane is the single source, no
double-paint — and point the arrow fill at `--depth-overlay-surface` so
it always matches the panel. Radius / font / color stay the panel's own.

Verified in-browser: open menu paints bg oklch(0.285) + 1px border +
shadow/halo from the plane; orphan-token contract test passes; check 0.

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

src/uix/eidos/components/dropdown-menu/README.md

@@ -140,11 +140,17 @@ chips" without per-item state bookkeeping.
 
 ## Decisiones
 
-- **No `variant` / `color` / `size` at the menu level.** Menus are
-  the visual variant of "list of actions" within an app; introducing
-  multiple visual flavors creates noise. If a consumer wants a colored
-  destructive item they pass `data-color` on the `<DropdownMenu.Item>`
-  directly (the morfo accepts it).
+- **No `variant` / `color` at the menu level.** Menus are the visual
+  variant of "list of actions" within an app; introducing multiple visual
+  flavors creates noise. If a consumer wants a colored destructive item they
+  pass `data-color` on the `<DropdownMenu.Item>` directly (the morfo accepts it).
+- **`size` IS a menu axis (1:1 with the controls).** A menu is *content*, so
+  it scales like a Field input — `size N → --font-size-N` + `--control-height-N`,
+  not one step below. `<DropdownMenu.Content size>` (default `md`) stamps
+  `data-size`; the recipe retints the panel's own per-size tokens, and the size
+  flows to every fly-out submenu via a context (submenus portal out, so CSS
+  inheritance can't carry it). This is what composed menus (e.g. `SplitButton`)
+  forward their size into — the scale lives here, once, not per consumer.
 - **Pass-through wrappers** for every part. Visual treatment is in the
   CSS recipe via `[data-dropdown-menu-*]` selectors — keeping wrappers
   thin makes context-menu and menubar trivial to derive (just

src/uix/eidos/components/dropdown-menu/dropdown-menu-content.svelte

@@ -34,7 +34,7 @@
 	setListSurfaceSizeContext({ getSize: () => resolvedSize });
 </script>
 
-<DropdownMenu.Content data-stagger="" data-list-surface="" {...rest} data-size={resolvedSize}>
+<DropdownMenu.Content data-stagger="" data-list-surface="" data-depth="overlay" {...rest} data-size={resolvedSize}>
 	{#snippet children(snippetProps)}
 		{@render bodyContent?.(snippetProps)}
 	{/snippet}

src/uix/eidos/components/dropdown-menu/dropdown-menu-sub-content.svelte

@@ -21,7 +21,7 @@
 	const resolvedSize = $derived(eidos.resolve(size ?? sizeCtx?.getSize(), 'md'));
 </script>
 
-<DropdownMenu.SubContent data-stagger="" data-list-surface="" {...rest} data-size={resolvedSize}>
+<DropdownMenu.SubContent data-stagger="" data-list-surface="" data-depth="overlay" {...rest} data-size={resolvedSize}>
 	{#snippet children(snippetProps)}
 		{@render bodyContent?.(snippetProps)}
 	{/snippet}

src/uix/eidos/components/dropdown-menu/dropdown-menu.css

@@ -36,11 +36,9 @@
 	max-block-size: var(--dropdown-menu-content-max-height, min(60vh, 22rem));
 	overflow-y: auto;
 	padding: var(--dropdown-menu-content-padding, var(--space-1));
-	border: var(--dropdown-menu-content-border-width, 1px) solid
-		var(--dropdown-menu-content-border-color, var(--color-border-default));
+	/* Elevation — surface · border · shadow — from the `overlay` plane via
+	   `data-depth` (A1, Decisión 8). Radius / font / color stay the panel's own. */
 	border-radius: var(--dropdown-menu-content-radius, var(--radius-md));
-	background: var(--dropdown-menu-content-bg, var(--color-surface-overlay));
-	box-shadow: var(--dropdown-menu-content-shadow, var(--shadow-overlay));
 	font-family: var(--style-label-font-family, var(--font-ui));
 	font-size: var(--dropdown-menu-content-font-size, var(--font-size-sm));
 	color: var(--color-content-primary);
@@ -182,7 +180,9 @@
 /* ── Arrow ────────────────────────────────────────────────────────── */
 
 [data-dropdown-menu-arrow] {
-	fill: var(--dropdown-menu-content-bg, var(--color-surface-overlay));
+	/* The arrow is part of the elevation surface — consume the `overlay` plane so
+	   it always matches the panel (A1, like popover), not a parallel token. */
+	fill: var(--depth-overlay-surface);
 }
 
 /* ── State transitions ────────────────────────────────────────────── */

src/uix/eidos/generated/base.css

@@ -3357,11 +3357,7 @@
 	--dropdown-menu-content-min-width: 12rem;
 	--dropdown-menu-content-max-height: min(60vh, 22rem);
 	--dropdown-menu-content-padding: var(--space-1);
-	--dropdown-menu-content-border-width: var(--border-width);
-	--dropdown-menu-content-border-color: var(--color-border-default);
 	--dropdown-menu-content-radius: var(--radius-md);
-	--dropdown-menu-content-bg: var(--color-surface-overlay);
-	--dropdown-menu-content-shadow: var(--depth-overlay-shadow), var(--depth-overlay-halo);
 	--dropdown-menu-content-font-size: var(--font-size-sm);
 	--dropdown-menu-item-gap: var(--space-2);
 	--dropdown-menu-item-height: 2rem;

src/uix/eidos/lib/recipes/base.ts

@@ -4196,11 +4196,7 @@ export const THEME_BASE_RECIPE_TOKENS = {
 		'content-min-width': '12rem',
 		'content-max-height': 'min(60vh, 22rem)',
 		'content-padding': 'var(--space-1)',
-		'content-border-width': 'var(--border-width)',
-		'content-border-color': 'var(--color-border-default)',
 		'content-radius': 'var(--radius-md)',
-		'content-bg': 'var(--color-surface-overlay)',
-		'content-shadow': 'var(--depth-overlay-shadow), var(--depth-overlay-halo)',
 		'content-font-size': 'var(--font-size-sm)',
 		'item-gap': 'var(--space-2)',
 		'item-height': '2rem',