feat(sacred-valley): card factory, registry ordering, view skeleton

Adds the Plan 6 card framework: svCard() chrome factory, pure orderCards()
ordering helper with unit tests, three stub card modules (clock/weather/host-perf),
and rewrites sacred_valley.js with the two-band layout that mounts ordered cards.

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

public/components/sv_card.js

@@ -0,0 +1,12 @@
+import { el } from '../dom.js';
+
+// Builds the refined-B chrome shell and returns { root, body }. The card module
+// fills `body` in its mount(); start()/stop() own its refresh timer.
+export function svCard(def) {
+  const body = el('div', { class: 'sv-card-body' });
+  const root = el('div', { class: 'sv-card', dataset: { size: def.size || 'm', cardId: def.id } },
+    el('div', { class: 'sv-card-title' }, def.title),
+    body
+  );
+  return { root, body };
+}