fix(eidos listbox): add max-block-size + overflow-y auto

The Listbox container grew unbounded when items overflowed — long lists
just stretched the parent layout. Adds:

- Default `max-block-size: min(60vh, 22rem)` via `--_listbox-max-height`
  token (consumer can override via inline style).
- `overflow-y: auto` + `overscroll-behavior: contain` so the listbox
  becomes its own scroll context.
- Horizontal orientation switches axes: removes the block cap and uses
  `overflow-x: auto` instead so a single-row list never clips.

Verified: with 8 items at md size, container caps at 352px with
scrollHeight 378px — scrollbar present and working.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/uix/eidos/components/listbox/listbox.css

@@ -21,6 +21,7 @@
 	--_listbox-item-height: var(--control-height-md);
 	--_listbox-item-px: var(--space-3);
 	--_listbox-item-font-size: var(--font-size-sm);
+	--_listbox-max-height: min(60vh, 22rem);
 	--_listbox-accent: var(--color-primary-solid);
 	--_listbox-accent-soft: var(--color-primary-element);
 	--_listbox-accent-text: var(--color-content-on-solid);
@@ -37,6 +38,15 @@
 	font-size: var(--_listbox-item-font-size);
 	line-height: var(--leading-ui);
 	outline: none;
+	/*
+	 * Vertical scroll for tall lists. Default cap is min(60vh, 22rem) —
+	 * generous but bounded. Consumer overrides via inline style
+	 * (e.g. `style="--_listbox-max-height: 40rem;"`) or by wrapping in a
+	 * fixed-height container.
+	 */
+	max-block-size: var(--_listbox-max-height);
+	overflow-y: auto;
+	overscroll-behavior: contain;
 }
 
 [data-listbox][data-block] {
@@ -48,6 +58,10 @@
 	flex-direction: row;
 	flex-wrap: wrap;
 	align-items: center;
+	/* Single row across the viewport — scroll inline, not block. */
+	max-block-size: none;
+	overflow-y: visible;
+	overflow-x: auto;
 }
 
 /* ── Variant — surface (default) ─ */