feat(link-preview, command): adopt the `overlay` elevation plane (B2)

Two more single-elevation overlays join the plane:

- link-preview: hover-card Content carries `data-depth="overlay"`; drop the
  hardcoded border / bg / shadow + point the arrow at `--depth-overlay-surface`.
- command: the palette panel carries `data-depth="overlay"`; drop its hardcoded
  border / bg / shadow. Inside `<Command.Dialog>` the existing
  `[data-dialog-content] [data-command]` override (higher specificity) strips
  the plane so the dialog panel stays the sole surface — no double-elevation.

Verified in-browser: link-preview + inline command paint bg oklch(0.285) + 1px
border + shadow/halo from the plane; command-in-dialog is stripped
(transparent / border 0 / shadow none); check 0.

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

src/uix/eidos/components/command/command.css

@@ -46,10 +46,11 @@
 	font-family: var(--font-ui);
 	line-height: var(--leading-ui);
 	color: var(--color-content-primary);
-	border: var(--border-width) solid var(--color-border-default);
+	/* Elevation — surface · border · shadow — from the `overlay` plane via
+	   `data-depth` (A1). Inside <Command.Dialog> the dialog panel is the surface,
+	   so the `[data-dialog-content] [data-command]` override below (higher
+	   specificity) strips the plane. Radius / overflow stay the panel's own. */
 	border-radius: var(--_command-radius);
-	background: var(--color-surface-overlay);
-	box-shadow: var(--depth-overlay-shadow), var(--depth-overlay-halo);
 	overflow: hidden;
 	outline: none;
 }

src/uix/eidos/components/command/command.svelte

@@ -69,7 +69,7 @@
 	});
 </script>
 
-<Command.Provider {...rest} bind:value bind:search data-list-surface="" data-size={resolvedSize}>
+<Command.Provider {...rest} bind:value bind:search data-list-surface="" data-depth="overlay" data-size={resolvedSize}>
 	{#snippet children(snippetProps)}
 		{@render bodyContent?.(snippetProps)}
 	{/snippet}

src/uix/eidos/components/link-preview/link-preview-content.svelte

@@ -22,7 +22,7 @@
 	const resolvedSize = $derived(eidos.resolve(size, 'md'));
 </script>
 
-<LinkPreview.Content {...rest} data-size={resolvedSize}>
+<LinkPreview.Content data-depth="overlay" {...rest} data-size={resolvedSize}>
 	{#snippet children(snippetProps)}
 		{@render bodyContent?.(snippetProps)}
 	{/snippet}

src/uix/eidos/components/link-preview/link-preview.css

@@ -60,11 +60,10 @@
 	min-inline-size: var(--_link-preview-min-width);
 	max-inline-size: var(--_link-preview-max-width);
 	padding: var(--_link-preview-py) var(--_link-preview-px);
-	border: var(--border-width) solid var(--color-border-default);
+	/* Elevation — surface · border · shadow — from the `overlay` plane via
+	   `data-depth` (A1, Decisión 8). Radius / color stay the panel's own. */
 	border-radius: var(--radius-md);
-	background: var(--color-surface-overlay);
 	color: var(--color-content-primary);
-	box-shadow: var(--depth-overlay-shadow), var(--depth-overlay-halo);
 	font-family: var(--font-ui);
 	font-size: var(--_link-preview-font-size);
 	font-weight: 400;
@@ -115,7 +114,9 @@
 
 /* ── Arrow ──────────────────────────────────────────────────────────── */
 [data-link-preview-arrow] {
-	fill: var(--color-surface-overlay);
+	/* Part of the elevation surface — consume the `overlay` plane so the arrow
+	   always matches the panel (A1, like popover). */
+	fill: var(--depth-overlay-surface);
 }
 
 /* ── State transitions per anchored side ────────────────────────────── */