feat(insights): chart cards for HRV, resting HR, SpO2, body temperature, active energy

Adds five sub-pages for the wave-A HealthKit metrics the server has
been storing since v1.4.23 / v1.4.25 but never surfaced on the web:

  - /insights/hrv               → HEART_RATE_VARIABILITY
  - /insights/ruhepuls          → RESTING_HEART_RATE
  - /insights/sauerstoff        → OXYGEN_SATURATION
  - /insights/koerpertemperatur → BODY_TEMPERATURE
  - /insights/aktive-energie    → ACTIVE_ENERGY_BURNED

Each page composes the shared `<HealthKitMetricPage>` scaffold —
`SubPageShell` + `HealthChartDynamic` mounted on its own
`ChartOverlayKey` slot + `CoachLaunchButton` + an empty-state CTA
that points at the existing `/measurements?add=<TYPE>` quick-entry
where a manual entry makes sense, or an Apple-Health-onboarding cue
otherwise. The five new chart-overlay-prefs slots (`hrv`,
`restingHr`, `oxygenSaturation`, `bodyTemperature`, `activeEnergy`)
let the chart-cog popover persist per metric.

Insights tab strip picks up the five new pills via the existing
`SUB_PAGE_METRIC` + `InsightMetric` enums. The wave-A categorisation
overlay realigns HRV + resting HR to the `cardiovascular` bucket
per the iOS handoff brief (PULSE stays in `vitals`; spot-pulse is a
point-in-time signal, derived heart-rate variants are the cardiac
risk surface). Six locales updated with the new sub-page titles,
descriptions, chart titles, and empty-state copy.

src/components/insights/healthkit-metric-page.tsx

@@ -0,0 +1,139 @@
+"use client";
+
+import Link from "next/link";
+import type { ComponentProps, ReactNode } from "react";
+
+import { useAuth } from "@/hooks/use-auth";
+import { useInsightsAnalytics } from "@/hooks/use-insights-analytics";
+import { useInsightsLayoutPrefs } from "@/hooks/use-insights-layout-prefs";
+import { useTranslations } from "@/lib/i18n/context";
+import type { InsightMetric } from "@/lib/insights/metric-availability";
+import type { ChartOverlayKey } from "@/lib/dashboard-layout";
+import { Button } from "@/components/ui/button";
+import { CoachLaunchButton } from "@/components/insights/coach-launch-button";
+import { HealthChartDynamic } from "@/components/charts/health-chart-dynamic";
+import { MetricEmptyState } from "@/components/insights/metric-empty-state";
+import { SubPageShell } from "@/components/insights/sub-page-shell";
+
+/**
+ * v1.4.32 — shared scaffold for the wave-A HealthKit metric pages.
+ *
+ * Each of the five new metric sub-pages (HRV, resting HR, oxygen
+ * saturation, body temperature, active energy) shares the same
+ * envelope:
+ *
+ *   1. `<SubPageShell>` with a localised title + description.
+ *   2. Empty-state CTA when the user has no observations for the
+ *      metric — points at `/measurements?add=<TYPE>` so the existing
+ *      quick-entry dialog can light up. The CTA target is optional;
+ *      Apple-Health-only metrics (active energy, body temperature)
+ *      pass `null` to render an onboarding hint without a dead link.
+ *   3. `<HealthChartDynamic>` mounted on the canonical
+ *      `ChartOverlayKey` so the chart-cog popover persists per metric.
+ *   4. `<CoachLaunchButton>` at the foot — feature-flag gating runs
+ *      inside the button so this scaffold stays agnostic.
+ *
+ * Adding a new metric is a four-line page module that hands the right
+ * Zod / MeasurementType + ChartOverlayKey + i18n-key prefix to this
+ * component; the template stays single-source-of-truth.
+ */
+
+export interface HealthKitMetricPageProps {
+  /** The MeasurementType that backs the chart. */
+  measurementType: string;
+  /** The InsightMetric key used by `useInsightsAnalytics()`. */
+  insightMetric: InsightMetric;
+  /** The chart-overlay slot id. */
+  chartKey: ChartOverlayKey;
+  /**
+   * i18n key prefix that drives `title`, `description`, `chartTitle`,
+   * `emptyState.title`, `emptyState.description`, `emptyState.cta`.
+   * Pages pass e.g. `"insights.hrv"` and the scaffold resolves each
+   * sub-key off the prefix.
+   */
+  i18nPrefix: string;
+  /** Single canonical colour for the chart line. */
+  color: string;
+  /** Unit suffix the chart renders next to the value. */
+  unit: string;
+  /** Optional y-axis label shown above the unit. */
+  yAxisUnit?: string;
+  /** Optional value bands (Apple-Health-style target zone shading). */
+  valueBands?: ComponentProps<typeof HealthChartDynamic>["valueBands"];
+  /**
+   * Optional empty-state CTA target. `null` renders the empty state
+   * without a primary action (Apple-Health-only metrics that have no
+   * manual entry form). String values land in `/measurements?add=<x>`.
+   */
+  emptyStateCtaType?: string | null;
+  /** Icon node mounted in the empty-state card. */
+  emptyStateIcon: ReactNode;
+  /**
+   * Optional Coach prefill for the empty-state launch. Falls back to a
+   * generic onboarding prompt threaded through `<CoachLaunchButton>`'s
+   * default.
+   */
+  coachPrefill?: string;
+}
+
+export function HealthKitMetricPage({
+  measurementType,
+  insightMetric,
+  chartKey,
+  i18nPrefix,
+  color,
+  unit,
+  yAxisUnit,
+  valueBands,
+  emptyStateCtaType,
+  emptyStateIcon,
+  coachPrefill,
+}: HealthKitMetricPageProps) {
+  const { user, isAuthenticated } = useAuth();
+  const { t } = useTranslations();
+  const { compareBaseline } = useInsightsLayoutPrefs(isAuthenticated);
+
+  const { isEmpty } = useInsightsAnalytics(insightMetric);
+
+  const title = t(`${i18nPrefix}.title`);
+  const description = t(`${i18nPrefix}.description`);
+
+  if (isEmpty) {
+    const ctaNode =
+      emptyStateCtaType != null ? (
+        <Button size="sm" asChild>
+          <Link href={`/measurements?add=${emptyStateCtaType}`}>
+            {t(`${i18nPrefix}.emptyState.cta`)}
+          </Link>
+        </Button>
+      ) : null;
+    return (
+      <SubPageShell title={title} description={description}>
+        <MetricEmptyState
+          icon={emptyStateIcon}
+          title={t(`${i18nPrefix}.emptyState.title`)}
+          description={t(`${i18nPrefix}.emptyState.description`)}
+          cta={ctaNode}
+          coachPrefill={coachPrefill ?? null}
+        />
+      </SubPageShell>
+    );
+  }
+
+  return (
+    <SubPageShell title={title} description={description}>
+      <HealthChartDynamic
+        chartKey={chartKey}
+        types={[measurementType]}
+        title={t(`${i18nPrefix}.chartTitle`)}
+        colors={[color]}
+        unit={unit}
+        yAxisUnit={yAxisUnit}
+        valueBands={valueBands}
+        compareBaseline={compareBaseline}
+        userTimezone={user?.timezone}
+      />
+      <CoachLaunchButton />
+    </SubPageShell>
+  );
+}