feat(insights): drive overview section + tile render from saved layout

Read the resolved insights layout on /insights and render the customizable
region from it. Sections render in saved order, hidden ones drop out, and
the Vitals grid honours the per-tile order + visibility. HeroStrip stays
anchored above the customizable region; every existing feature/data gate
(briefing flag, cycle-enabled, per-tile data) still applies on top, so the
default layout reproduces the prior page.

- useInsightsLayout() reads GET /api/insights/layout through the query-key
  factory, defaulting to DEFAULT_INSIGHTS_LAYOUT while in flight.
- orderedVisibleSectionIds + resolveTileLayout: pure, unit-tested helpers.
- Widen DEFAULT_VISIBLE_TILE_IDS with the Vitals/Mobility grid tiles so a
  fresh account keeps the tiles it shows today.

src/hooks/use-insights-layout.ts

@@ -0,0 +1,39 @@
+"use client";
+
+import { useQuery } from "@tanstack/react-query";
+
+import { queryKeys } from "@/lib/query-keys";
+import {
+  DEFAULT_INSIGHTS_LAYOUT,
+  resolveInsightsLayout,
+  type InsightsLayout,
+} from "@/lib/insights-layout";
+
+/**
+ * v1.15.11 W2 — the resolved insights overview layout (sections + tiles).
+ *
+ * Reads `GET /api/insights/layout` through the centralised query-key factory
+ * (`queryKeys.insightsLayout()` → `["user","insightsLayout"]`), the same key
+ * the W3 PUT mutation invalidates on save so the overview repaints in
+ * lockstep with the Settings / inline-edit surfaces. The response is already
+ * the server-resolved v2 layout; we pass it back through
+ * `resolveInsightsLayout` defensively so a partial / legacy blob from a stale
+ * cache still normalises to a valid `InsightsLayout`.
+ *
+ * Returns `DEFAULT_INSIGHTS_LAYOUT` while the query is in-flight so the page
+ * renders in the default section + tile order on first paint — no layout
+ * flicker, no empty state, no "everything hidden" flash before the saved
+ * layout lands.
+ */
+export function useInsightsLayout(enabled: boolean): InsightsLayout {
+  const { data } = useQuery({
+    queryKey: queryKeys.insightsLayout(),
+    queryFn: async () => {
+      const res = await fetch("/api/insights/layout");
+      if (!res.ok) throw new Error("Failed to load insights layout");
+      return resolveInsightsLayout((await res.json()).data);
+    },
+    enabled,
+  });
+  return data ?? DEFAULT_INSIGHTS_LAYOUT;
+}