feat(accordion): align with Base UI API, fix data-disabled bugs, refactor stories

  New inputs/outputs (Base UI alignment):
  - `multiple: boolean` on root (takes precedence over `type`, which stays for compat)
  - `loopFocus: boolean` on root (default true), wired into useArrowNavigation
  - `onOpenChange: output<boolean>` on item (skips initial render)
  - `data-index` on all parts: item, header, trigger, content
  - `data-panel-open` on trigger for open-state CSS styling
  - `data-disabled` on root

  Bug fixes:
  - content/header were binding boolean `false` to data-disabled instead of removing the attribute
  - item data-disabled used item-level `disabled()` only, ignoring root disabled state

Author: pimenovoleg

apps/radix-storybook/.storybook/tailwind.css

@@ -126,6 +126,51 @@
     --animate-popover-popup-out: popover-popup-out 120ms ease-in;
     --animate-popover-viewport-in: popover-viewport-in 200ms ease-out;
     --animate-popover-viewport-out: popover-viewport-out 200ms ease-in;
+
+    --animate-accordion-down: accordion-down 200ms ease-out;
+    --animate-accordion-up: accordion-up 200ms ease-out;
+    --animate-accordion-right: accordion-right 200ms ease-out;
+    --animate-accordion-left: accordion-left 200ms ease-out;
+}
+
+@keyframes accordion-down {
+    from {
+        height: 0;
+    }
+
+    to {
+        height: var(--radix-accordion-content-height);
+    }
+}
+
+@keyframes accordion-up {
+    from {
+        height: var(--radix-accordion-content-height);
+    }
+
+    to {
+        height: 0;
+    }
+}
+
+@keyframes accordion-right {
+    from {
+        width: 0;
+    }
+
+    to {
+        width: var(--radix-accordion-content-width);
+    }
+}
+
+@keyframes accordion-left {
+    from {
+        width: var(--radix-accordion-content-width);
+    }
+
+    to {
+        width: 0;
+    }
 }
 
 @keyframes popover-in {