Fix Tooltip overflow-hidden clipping via portal action

Portal the tooltip into document.body so overflow:hidden ancestors
can't clip it. Fixed positioning + getBoundingClientRect() for placement.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/lib/ui/Tooltip.svelte

@@ -49,6 +49,14 @@
       ? `position:fixed;top:${fixedTop}px;left:${fixedLeft}px;transform:translateY(-100%);`
       : `position:fixed;top:${fixedTop}px;left:${fixedLeft}px;`,
   );
+
+  // Portal action: moves the node into document.body so overflow:hidden ancestors can't clip it.
+  function portal(node: HTMLElement) {
+    document.body.appendChild(node);
+    return {
+      destroy() { node.remove(); },
+    };
+  }
 </script>
 
 <div
@@ -63,6 +71,7 @@
   {@render children?.()}
   {#if showTooltip}
     <div
+      use:portal
       role="tooltip"
       class="z-[9999] px-3 py-2 text-xs font-normal text-stein-0 bg-stein-800 rounded-xs shadow-lg min-w-56 max-w-88 text-center pointer-events-none whitespace-normal"
       style={tooltipStyle}