feat(ui): build Scrollspy, fix aria-current across the navigation group

Scrollspy replaces a scaffold that rendered bare anchors. The runtime observes
the sections the links point at and writes the marker straight onto the links:
an IntersectionObserver callback fires long after the client function that
registered it returned, so a state write there would be dropped.

Navbar and Breadcrumb both emitted aria-current="" for every inactive link.
That is not a valid value -- the attribute takes a token or must be absent --
so every link claimed a state it did not have. Breadcrumb had it too, despite
being the strongest component in the group.

Navbar also takes roving arrow-key focus across its menu bar.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

packages/ui/components/Scrollspy.wrn

@@ -1,21 +1,172 @@
+// Scrollspy -- a table of contents that follows the reader.
+//
+//   <Scrollspy items='[{"label":"Overview","href":"#overview"}]' />
+//
+// Each href points at an element on the page. The runtime observes those
+// elements and moves aria-current to the link for whichever one is in view.
+//
+// The runtime writes the marker straight onto the links rather than into
+// component state. An IntersectionObserver callback fires long after the
+// client function that registered it has returned, and a state write made
+// there is dropped -- so the DOM is the only place the answer can live.
+//
+// NOTE: the style block uses /* */ comments only -- // is not a CSS comment
+// and silently swallows the rule that follows it.
 component Scrollspy {
   outputs {
-    change(payload: { value?: string | number | boolean | null; values?: Array<string | number | boolean | null | object>; sourceEvent?: Event; [key: string]: string | number | boolean | null | object } | string | number | boolean | null)
+    change(payload: { href: string; label: string })
   }
 
   props {
-size: string = "default"
     color: string = "primary"
-    label: string = "Scrollspy"
+    size: string = "default"
     items: unknown[] = []
     active: string = ""
-    orientation: string = "horizontal"
+    label: string = "On this page"
+    heading: string = ""
     class: string = ""
   }
+
+  functions {
+    shared function itemList() {
+      return Array.isArray(items) ? items : []
+    }
+
+    shared function isActive(item) {
+      return Boolean(item.href) && item.href === active
+    }
+  }
+
   view {
-    <nav class="wire-next wire-next--color-{color} wire-next--size-{size} wire-next--scrollspy wire-next--{orientation} {class}" aria-label="{label}">
-      {#each items as item}<a href="{item.href}" aria-current="{item.value === active ? 'page' : ''}">{item.label}</a>{/each}
+    <nav
+      {...attrs}
+      data-ui-component="Scrollspy"
+      class='wire-scrollspy {class}'
+      data-color='{color}'
+      data-size='{size}'
+      data-wrn-scrollspy="true"
+      role="navigation"
+      aria-label='{label}'
+    >
+      <p class="wire-scrollspy__heading" data-show="heading">{heading}</p>
+
+      <ul class="wire-scrollspy__list">
+        {#each itemList() as item}
+          <li class="wire-scrollspy__item">
+            <a
+              class="wire-scrollspy__link"
+              href='{item.href || "#"}'
+              data-active='{isActive(item)}'
+              aria-current='{isActive(item) ? "location" : "false"}'
+            >
+              <span class="wire-scrollspy__label">{item.label}</span>
+            </a>
+          </li>
+        {/each}
+      </ul>
+
       <slot />
     </nav>
   }
+
+  style {
+    .wire-scrollspy {
+      --scrollspy-accent: var(--wire-color-primary);
+      max-width: 100%;
+    }
+
+    .wire-scrollspy[data-color="secondary"] {
+      --scrollspy-accent: var(--wire-color-secondary);
+    }
+
+    .wire-scrollspy[data-color="success"] {
+      --scrollspy-accent: var(--wire-color-success);
+    }
+
+    .wire-scrollspy[data-color="danger"] {
+      --scrollspy-accent: var(--wire-color-danger);
+    }
+
+    .wire-scrollspy[data-color="info"] {
+      --scrollspy-accent: var(--wire-color-info);
+    }
+
+    .wire-scrollspy[data-size="sm"] {
+      font-size: 0.82rem;
+    }
+
+    .wire-scrollspy[data-size="lg"] {
+      font-size: 1rem;
+    }
+
+    .wire-scrollspy__heading {
+      margin: 0 0 0.5rem;
+      color: var(--wire-color-text-muted);
+      font-size: 0.72rem;
+      font-weight: 700;
+      letter-spacing: 0.08em;
+      text-transform: uppercase;
+    }
+
+    .wire-scrollspy__list {
+      display: grid;
+      gap: 0.1rem;
+      margin: 0;
+      padding: 0;
+      list-style: none;
+      border-left: 1px solid var(--wire-color-border);
+    }
+
+    .wire-scrollspy__link {
+      display: block;
+      padding: 0.3rem 0.75rem;
+      margin-left: -1px;
+      border-left: 2px solid transparent;
+      color: var(--wire-color-text-muted);
+      font-size: 0.85rem;
+      text-decoration: none;
+    }
+
+    .wire-scrollspy__link:hover {
+      color: var(--wire-color-text);
+    }
+
+    .wire-scrollspy__link:focus-visible {
+      outline: 2px solid var(--scrollspy-accent);
+      outline-offset: -2px;
+    }
+
+    .wire-scrollspy__link[data-active="true"] {
+      border-left-color: var(--scrollspy-accent);
+      color: var(--scrollspy-accent);
+      font-weight: 600;
+    }
+
+    /*
+     * A table of contents is a sidebar affordance. On a phone it stops being
+     * a rail and becomes a horizontal strip that scrolls, so it costs one
+     * line rather than a screenful.
+     */
+    @media (max-width: 767px) {
+      .wire-scrollspy__list {
+        grid-auto-flow: column;
+        grid-auto-columns: max-content;
+        overflow-x: auto;
+        border-left: 0;
+        border-bottom: 1px solid var(--wire-color-border);
+      }
+
+      .wire-scrollspy__link {
+        margin-left: 0;
+        border-left: 0;
+        border-bottom: 2px solid transparent;
+        white-space: nowrap;
+      }
+
+      .wire-scrollspy__link[data-active="true"] {
+        border-left-color: transparent;
+        border-bottom-color: var(--scrollspy-accent);
+      }
+    }
+  }
 }