refactor(cycle): wire the phase-correlation card into the insights tab

The cycle insights tab rendered an empty placeholder while the phase-contrast
card + its `/api/cycle/insights` feed sat unused. Wire them together: a
`useCycleInsights` read drives the headline finding + the luteal-vs-follicular
crosstab on the insights tab, matching the mood-factor crosstab styling. Drops
the placeholder card + a duplicate disclaimer component in favour of the ones
already in use, and removes the unused recency/phase-result/label exports.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/components/cycle/__tests__/cycle-insights.test.tsx

@@ -1,43 +0,0 @@
-import { describe, it, expect } from "vitest";
-import { renderToStaticMarkup } from "react-dom/server";
-
-import { CycleInsights } from "../cycle-insights";
-import { I18nProvider } from "@/lib/i18n/context";
-
-function render(node: React.ReactNode) {
-  return renderToStaticMarkup(
-    <I18nProvider initialLocale="en">{node}</I18nProvider>,
-  );
-}
-
-describe("<CycleInsights>", () => {
-  it("renders the empty-state when no cards are surfaced", () => {
-    const html = render(<CycleInsights cards={[]} />);
-    expect(html).toContain("Phase insights appear here");
-    expect(html).not.toContain('data-slot="cycle-insights"');
-  });
-
-  it("renders the card list with the open statistics when cards are present", () => {
-    const html = render(
-      <CycleInsights
-        cards={[
-          {
-            id: "rhr-luteal",
-            title: "Resting heart rate runs higher in your luteal phase",
-            body: "Across your logged cycles RHR is ~3 bpm higher in luteal vs follicular days.",
-            n: 42,
-            effectSize: 0.61,
-            qValue: 0.04,
-            caveat: "Descriptive only.",
-          },
-        ]}
-      />,
-    );
-    expect(html).toContain('data-slot="cycle-insights"');
-    expect(html).toContain("Resting heart rate runs higher");
-    expect(html).toContain("n = 42");
-    expect(html).toContain("0.61");
-    expect(html).toContain("0.040");
-    expect(html).toContain("Descriptive only.");
-  });
-});