feat(ui): build the Stepper component

Replaces a scaffold that rendered bare anchors with ordered steps: complete,
current and upcoming status derived from the active index, horizontal or
vertical, optional icons, and indexed named slots (step-0, step-1, ...) for
authoring a step body by hand.

Also tightens the roving contract from the previous commit. A template writes
data-wrn-roving="" or data-wrn-roving-item="false" to mean not this time, but
a bare [attr] selector matches either, so a read-only stepper would still have
taken arrow-key focus. The container now requires a named axis, while a bare
item marker still counts as opted in.

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

examples/component-showcase/scripts/showcase-profiles.mjs

@@ -253,6 +253,44 @@ const DATATABLE_ROWS =
   '[{"id": 1, "name": "Northwind", "plan": "Scale", "owner": "A. Okafor", "seats": 6, "status": "Active", "statusHtml": "<span class=\\"showcase-pill showcase-pill--success\\">Active</span>"}, {"id": 2, "name": "Acme Industrial", "plan": "Team", "owner": "R. Silva", "seats": 13, "status": "Trial", "statusHtml": "<span class=\\"showcase-pill showcase-pill--info\\">Trial</span>"}, {"id": 3, "name": "Globex", "plan": "Enterprise", "owner": "M. Chen", "seats": 20, "status": "Past due", "statusHtml": "<span class=\\"showcase-pill showcase-pill--danger\\">Past due</span>"}, {"id": 4, "name": "Initech", "plan": "Starter", "owner": "J. Dubois", "seats": 27, "status": "Active", "statusHtml": "<span class=\\"showcase-pill showcase-pill--success\\">Active</span>"}, {"id": 5, "name": "Umbrella", "plan": "Scale", "owner": "P. Novak", "seats": 34, "status": "Trial", "statusHtml": "<span class=\\"showcase-pill showcase-pill--info\\">Trial</span>"}, {"id": 6, "name": "Stark Labs", "plan": "Team", "owner": "A. Okafor", "seats": 41, "status": "Past due", "statusHtml": "<span class=\\"showcase-pill showcase-pill--danger\\">Past due</span>"}, {"id": 7, "name": "Wayne Foods", "plan": "Enterprise", "owner": "R. Silva", "seats": 48, "status": "Active", "statusHtml": "<span class=\\"showcase-pill showcase-pill--success\\">Active</span>"}, {"id": 8, "name": "Soylent", "plan": "Starter", "owner": "M. Chen", "seats": 55, "status": "Trial", "statusHtml": "<span class=\\"showcase-pill showcase-pill--info\\">Trial</span>"}, {"id": 9, "name": "Hooli", "plan": "Scale", "owner": "J. Dubois", "seats": 62, "status": "Past due", "statusHtml": "<span class=\\"showcase-pill showcase-pill--danger\\">Past due</span>"}, {"id": 10, "name": "Vehement", "plan": "Team", "owner": "P. Novak", "seats": 69, "status": "Active", "statusHtml": "<span class=\\"showcase-pill showcase-pill--success\\">Active</span>"}, {"id": 11, "name": "Massive Dynamic", "plan": "Enterprise", "owner": "A. Okafor", "seats": 76, "status": "Trial", "statusHtml": "<span class=\\"showcase-pill showcase-pill--info\\">Trial</span>"}, {"id": 12, "name": "Cyberdyne", "plan": "Starter", "owner": "R. Silva", "seats": 83, "status": "Past due", "statusHtml": "<span class=\\"showcase-pill showcase-pill--danger\\">Past due</span>"}, {"id": 13, "name": "Tyrell", "plan": "Scale", "owner": "M. Chen", "seats": 90, "status": "Active", "statusHtml": "<span class=\\"showcase-pill showcase-pill--success\\">Active</span>"}, {"id": 14, "name": "Aperture", "plan": "Team", "owner": "J. Dubois", "seats": 97, "status": "Trial", "statusHtml": "<span class=\\"showcase-pill showcase-pill--info\\">Trial</span>"}, {"id": 15, "name": "Black Mesa", "plan": "Enterprise", "owner": "P. Novak", "seats": 104, "status": "Past due", "statusHtml": "<span class=\\"showcase-pill showcase-pill--danger\\">Past due</span>"}]';
 
 export const componentProfiles = {
+  Stepper: {
+    demos: [
+      standard(
+        "Horizontal progress",
+        "Steps before the active one read as complete, the active one is highlighted, and the rest are muted.",
+        {
+          steps: [
+            { label: "Account", description: "Your details" },
+            { label: "Billing", description: "Payment method" },
+            { label: "Confirm", description: "Review and submit" },
+          ],
+          active: 1,
+        },
+      ),
+      standard(
+        "Vertical with icons",
+        "Vertical orientation suits a sidebar or a narrow column. Any step may carry an iconify class instead of its number.",
+        {
+          steps: [
+            { label: "Cloned", icon: "icon-[lucide--git-branch]" },
+            { label: "Built", icon: "icon-[lucide--hammer]" },
+            { label: "Deployed", icon: "icon-[lucide--rocket]" },
+          ],
+          active: 2,
+          orientation: "vertical",
+        },
+      ),
+      advanced(
+        "Clickable steps",
+        "With clickable the steps emit a change output and take arrow-key roving focus. Without it the stepper is read-only and stays out of the tab order.",
+        {
+          steps: [{ label: "One" }, { label: "Two" }, { label: "Three" }],
+          active: 0,
+          clickable: true,
+        },
+      ),
+    ],
+  },
   Pagination: {
     demos: [
       standard(