refactor(frontend): migrate agent stat-window selector to createTabStrip (#1464 step 1)

Replaces the agent stats page's bespoke window-tab click handler with the
shared createTabStrip (@hive/shared/tabs.js). The selector is now
hash-routed — #1h / #24h / … become deep-linkable and survive
back/forward navigation.

- window buttons use data-tab (was data-w); the strip resolves them by
  that convention and toggles .hive-tab--active + aria-selected.
- onShow(w) sets currentWindow + reloads stats; the strip's initial show
  fires it once, so the explicit loadStats() in DOMContentLoaded is
  dropped (avoids a double fetch).
- the selector keeps its distinct pill look — agent.css now targets
  .window-tabs button.hive-tab--active (was .active), not the shared
  .hive-tab text-tab base. It's a pure data-selector with no panes;
  createTabStrip skips the absent [data-tab-pane] gracefully.

Behaviour-preserving; aria-selected is now standardised on the buttons.

frontend/packages/agent/src/stats.js

@@ -3,6 +3,7 @@
 // when the operator clicks a window tab.
 
 import Chart from 'chart.js/auto';
+import { createTabStrip } from '@hive/shared/tabs.js';
 
 // Expose for the IIFE below — pre-split this was a window global from
 // the jsDelivr CDN script tag. esbuild now bundles chart.js into
@@ -413,20 +414,15 @@ window.Chart = Chart;
     } catch (_) { /* non-fatal */ }
   }
 
-  function bindTabs() {
-    const tabs = document.getElementById('window-tabs');
-    tabs.addEventListener('click', (ev) => {
-      const btn = ev.target.closest('button[data-w]');
-      if (!btn) return;
-      currentWindow = btn.dataset.w;
-      for (const b of tabs.querySelectorAll('button')) b.classList.toggle('active', b === btn);
-      loadStats();
-    });
-  }
-
   document.addEventListener('DOMContentLoaded', () => {
-    bindTabs();
     loadIdentity();
-    loadStats();
+    // The shared hash-routed tab strip drives the stat-window selector,
+    // making it deep-linkable (#1h / #24h / …). onShow updates the
+    // window + reloads; the strip's initial show fires onShow once, so
+    // there's no separate loadStats() call here (avoids a double fetch).
+    createTabStrip(document.getElementById('window-tabs'), {
+      defaultId: currentWindow,
+      onShow: (w) => { currentWindow = w; loadStats(); },
+    });
   });
 })();