feat(cycle): cycle-phase correlation insight + Coach phase dimension

Add the menstrual-cycle phase as a channel in the existing FDR-guarded
correlation machinery, the same way rated mood factors were folded in —
no new statistics, the same Welch + Benjamini-Hochberg pipeline, the same
day floors and q = 0.10 gate.

Two complementary mechanisms, both confined to a gender-gated surface:
- a categorical luteal-vs-follicular contrast per outcome metric (resting
  heart rate, HRV, sleep, steps, weight, basal/wrist/skin temperature),
  surfacing one headline finding (resting-heart-rate-by-phase, falling
  back to HRV); and
- the continuous phase ordinal folded into the lagged-Pearson matrix.

Phase never reaches the general correlations route — the temperature
channels held out of the general matrix are un-blocked only here, behind
the cycle gate, so a reproductive inference can never leak onto a
non-gated surface. Every row shows n, effect size, p and q; nothing is
fabricated on thin data and nothing is framed as causal.

Surface it through a new gated GET /api/cycle/insights and a drop-in
card that mirrors the mood-factor crosstab.

Add a cycle dimension to the Coach snapshot: current phase + day-of-cycle,
the next predicted event (period range + confidence + method, fertile
window goal-gated), and the headline phase finding — present only for a
cycle-enabled account, so a non-cycle snapshot is unchanged. A new ground
rule keeps the Coach descriptive: never contraception-grade, never a
"safe day" claim.

OpenAPI regenerated; phase-correlation + snapshot-inclusion tests added;
copy localised across all six locales.

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

src/components/cycle/cycle-phase-crosstab.tsx

@@ -0,0 +1,202 @@
+"use client";
+
+import { useTranslations } from "@/lib/i18n/context";
+import { cn } from "@/lib/utils";
+
+/**
+ * v1.15 — CYCLE_PHASE × vital crosstab card.
+ *
+ * Mirrors the mood-factor × vital crosstab (`mood-factor-metric-crosstab.tsx`):
+ * for each outcome metric, the vital's mean on LUTEAL-phase days vs
+ * FOLLICULAR-phase days, the signed delta, n per group, q, and a confidence
+ * chip. The math is pre-computed in `src/lib/cycle/phase-crosstab.ts`
+ * (`computePhaseMetricCrosstab`) — the same Welch t-test + day floors +
+ * Benjamini-Hochberg FDR the rest of the relations surface uses; only
+ * FDR-surviving rows reach here. Observational only — the page-level
+ * "associations, not causes" footer carries the caveat once. This surface is
+ * gender-gated by its `/api/cycle/insights` route; phase never renders on the
+ * general correlations surface.
+ */
+
+export type CyclePhaseCrosstabDisplay =
+  | "hours"
+  | "steps"
+  | "bpm"
+  | "ms"
+  | "kg"
+  | "celsius";
+
+export type CyclePhaseCrosstabConfidence = "low" | "medium" | "high";
+
+export interface CyclePhaseCrosstabRow {
+  metricKey: string;
+  display: CyclePhaseCrosstabDisplay;
+  lutealDays: number;
+  follicularDays: number;
+  lutealAvg: number;
+  follicularAvg: number;
+  delta: number;
+  pValue: number;
+  qValue: number;
+  confidence: CyclePhaseCrosstabConfidence;
+}
+
+const METRIC_LABEL_KEY: Record<string, string> = {
+  restingHeartRate: "cycle.insights.crosstab.metricRestingHeartRate",
+  heartRateVariability: "cycle.insights.crosstab.metricHrv",
+  sleepDuration: "cycle.insights.crosstab.metricSleepDuration",
+  steps: "cycle.insights.crosstab.metricSteps",
+  weight: "cycle.insights.crosstab.metricWeight",
+  basalBodyTemp: "cycle.insights.crosstab.metricBasalBodyTemp",
+  wristTemperature: "cycle.insights.crosstab.metricWristTemperature",
+  skinTemperature: "cycle.insights.crosstab.metricSkinTemperature",
+};
+
+const UNIT_KEY: Record<CyclePhaseCrosstabDisplay, string> = {
+  hours: "cycle.insights.crosstab.unitHours",
+  steps: "cycle.insights.crosstab.unitSteps",
+  bpm: "cycle.insights.crosstab.unitBpm",
+  ms: "cycle.insights.crosstab.unitMs",
+  kg: "cycle.insights.crosstab.unitKg",
+  celsius: "cycle.insights.crosstab.unitCelsius",
+};
+
+const CONFIDENCE_KEY: Record<CyclePhaseCrosstabConfidence, string> = {
+  low: "cycle.insights.crosstab.confidenceLow",
+  medium: "cycle.insights.crosstab.confidenceMedium",
+  high: "cycle.insights.crosstab.confidenceHigh",
+};
+
+const CONFIDENCE_CLASS: Record<CyclePhaseCrosstabConfidence, string> = {
+  low: "bg-secondary text-muted-foreground",
+  medium: "bg-info/15 text-info",
+  high: "bg-success/15 text-success",
+};
+
+/** Whole numbers for steps; one decimal otherwise. */
+function fmt(value: number, display: CyclePhaseCrosstabDisplay): string {
+  return display === "steps" ? Math.round(value).toString() : value.toFixed(1);
+}
+
+const HEADLINE_KEY: Record<string, string> = {
+  restingHeartRate: "cycle.insights.headline.restingHeartRate",
+  heartRateVariability: "cycle.insights.headline.heartRateVariability",
+};
+
+/**
+ * The single headline finding rendered prominently above the grid. Resting
+ * heart rate / HRV get bespoke phrasing; every other metric uses the generic
+ * line. Returns null when nothing cleared the FDR gate — an honest empty state.
+ */
+export function CyclePhaseHeadline({
+  headline,
+}: {
+  headline: CyclePhaseCrosstabRow | null;
+}) {
+  const { t } = useTranslations();
+  if (!headline) {
+    return (
+      <p
+        data-slot="cycle-phase-headline-empty"
+        className="text-muted-foreground text-sm"
+      >
+        {t("cycle.insights.headline.empty")}
+      </p>
+    );
+  }
+  const metricLabel = t(METRIC_LABEL_KEY[headline.metricKey] ?? headline.metricKey);
+  const unit = t(UNIT_KEY[headline.display]);
+  const up = headline.delta >= 0;
+  const dir = t(
+    up ? "cycle.insights.headline.dirHigher" : "cycle.insights.headline.dirLower",
+  );
+  const params = {
+    metric: metricLabel,
+    delta: fmt(Math.abs(headline.delta), headline.display),
+    unit,
+    dir,
+  };
+  const key = HEADLINE_KEY[headline.metricKey] ?? "cycle.insights.headline.generic";
+  return (
+    <p
+      data-slot="cycle-phase-headline"
+      data-metric={headline.metricKey}
+      className="text-foreground text-sm font-medium"
+    >
+      {t(key, params)}
+    </p>
+  );
+}
+
+export function CyclePhaseCrosstab({
+  rows,
+}: {
+  rows: CyclePhaseCrosstabRow[];
+}) {
+  const { t } = useTranslations();
+  if (rows.length === 0) return null;
+
+  return (
+    <div data-slot="cycle-phase-crosstab">
+      <p className="text-muted-foreground mb-2 text-sm">
+        {t("cycle.insights.crosstab.description")}
+      </p>
+      <ul className="divide-border divide-y">
+        {rows.map((row) => {
+          const metricLabel = t(METRIC_LABEL_KEY[row.metricKey] ?? row.metricKey);
+          const unit = t(UNIT_KEY[row.display]);
+          // `delta` = lutealAvg − follicularAvg: positive = the vital runs
+          // higher in the luteal phase. The number stays NEUTRAL — higher is
+          // good for steps but bad for resting HR, and this board is
+          // observational, so colouring it would imply a verdict the data
+          // doesn't support. The sign prefix + `data-direction` carry it.
+          const up = row.delta >= 0;
+          const deltaText = `${up ? "+" : ""}${fmt(row.delta, row.display)} ${unit}`;
+          return (
+            <li
+              key={row.metricKey}
+              className="flex flex-col gap-1.5 py-2"
+              data-slot="cycle-phase-crosstab-row"
+              data-metric={row.metricKey}
+              data-direction={up ? "up" : "down"}
+              data-confidence={row.confidence}
+            >
+              <div className="flex items-center gap-2 text-sm">
+                <span
+                  className="text-foreground min-w-0 flex-1 truncate"
+                  title={metricLabel}
+                >
+                  {t("cycle.insights.crosstab.pairLabel", { metric: metricLabel })}
+                </span>
+                <span className="text-foreground shrink-0 text-sm font-semibold tabular-nums">
+                  {deltaText}
+                </span>
+                <span
+                  className={cn(
+                    "shrink-0 rounded-full px-2 py-0.5 text-[10px] font-medium",
+                    CONFIDENCE_CLASS[row.confidence],
+                  )}
+                >
+                  {t(CONFIDENCE_KEY[row.confidence])}
+                </span>
+              </div>
+              <p className="text-muted-foreground text-xs">
+                {t("cycle.insights.crosstab.detail", {
+                  metric: metricLabel,
+                  lutealAvg: fmt(row.lutealAvg, row.display),
+                  follicularAvg: fmt(row.follicularAvg, row.display),
+                  unit,
+                  lutealDays: row.lutealDays,
+                  follicularDays: row.follicularDays,
+                })}
+              </p>
+            </li>
+          );
+        })}
+      </ul>
+      <p className="text-muted-foreground mt-3 text-xs">
+        {t("cycle.insights.crosstab.footer")}
+      </p>
+    </div>
+  );
+}