feat: explainable longitudinal pattern summaries with cited records (#34)

The home insight card now reports the confirmed-log count and form
groupings for a window, every line names the exact confirmed records it
was built from, and following a citation opens those records. A window
below the minimum states that it is too sparse instead of describing a
trend, and a window with both firm and loose logs says it is mixed rather
than picking a winner. No line explains a cause, rules on food, or offers
a health verdict.

- src/summary.js: window filtering, insufficient-data guard, per-form
  lines, mixed-pattern line, boundary copy, record citations
- app.js: explainable home card plus a pattern-source sheet listing the
  cited records
- tests/summary.test.js, tests/pattern-summary.acceptance.mjs: unit and
  real-browser coverage, gated in CI and the release builder
- scripts/record_release_demo.mjs: fictional multi-day sample logs,
  citation follow-through, and the sparse-window refusal on camera

src/summary.js

@@ -0,0 +1,76 @@
+import { bucketForBristolType } from './domain.js';
+
+export const PATTERN_WINDOW_DAYS = 28;
+// Two logs are an anecdote. Below this the summary is required to say so instead of describing a trend.
+export const MIN_WINDOW_LOGS = 3;
+
+const DAY_MS = 86400000;
+
+// The summary may only describe what the user recorded. No cause, no health verdict, no food ruling.
+const BOUNDARY = 'Built only from your own confirmed records in this window. Timmy reports what you logged and when — not why, and never a verdict on your health or your food.';
+
+function inWindowRecords(entries, now, windowDays) {
+  const startedAt = now - windowDays * DAY_MS;
+  return (Array.isArray(entries) ? entries : [])
+    .map(entry => ({ entry, at: new Date(entry?.occurredAt).getTime() }))
+    .filter(({ at }) => Number.isFinite(at) && at <= now && at >= startedAt)
+    .sort((left, right) => left.at - right.at)
+    .map(({ entry, at }) => ({
+      id: String(entry?.id ?? ''),
+      occurredAt: new Date(at).toISOString(),
+      bristolType: Number(entry?.bristolType),
+      bucket: bucketForBristolType(entry?.bristolType),
+    }));
+}
+
+export function buildPatternSummary(entries = [], { now = Date.now(), windowDays = PATTERN_WINDOW_DAYS } = {}) {
+  const records = inWindowRecords(entries, now, windowDays);
+  const window = {
+    days: windowDays,
+    label: `last ${windowDays} days`,
+    start: new Date(now - windowDays * DAY_MS).toISOString(),
+    end: new Date(now).toISOString(),
+  };
+
+  if (records.length < MIN_WINDOW_LOGS) {
+    return {
+      window,
+      records,
+      insufficient: true,
+      statements: [],
+      boundary: BOUNDARY,
+      copy: `Not enough confirmed logs in this window yet — ${records.length} of ${MIN_WINDOW_LOGS} needed before Timmy describes a pattern.`,
+    };
+  }
+
+  const frequency = {
+    id: 'frequency',
+    text: `${records.length} confirmed log${records.length === 1 ? '' : 's'} in the ${window.label}.`,
+    entryIds: records.map(record => record.id),
+  };
+
+  const buckets = new Map();
+  for (const record of records) {
+    if (!buckets.has(record.bucket)) buckets.set(record.bucket, []);
+    buckets.get(record.bucket).push(record.id);
+  }
+  const bucketLine = (bucket, label) => ({
+    id: bucket === 'constipation' ? 'firm' : bucket,
+    text: `${label}: ${buckets.get(bucket).length} of ${records.length} confirmed log${records.length === 1 ? '' : 's'}.`,
+    entryIds: buckets.get(bucket),
+  });
+  const formLines = [
+    ['constipation', 'Firm side (Type 1–2)'],
+    ['typical', 'Typical range (Type 3–4)'],
+    ['loose', 'Loose side (Type 5–7)'],
+  ].filter(([bucket]) => buckets.has(bucket)).map(([bucket, label]) => bucketLine(bucket, label));
+  // Both ends in one window is not a trend, and the summary has to say so out loud rather than
+  // picking whichever side is marginally larger.
+  const mixedLine = buckets.has('constipation') && buckets.has('loose') ? [{
+    id: 'mixed',
+    text: `Firm and loose logs both appear in the ${window.label} (${buckets.get('constipation').length} firm, ${buckets.get('loose').length} loose), which is a mixed pattern and not one trend.`,
+    entryIds: records.filter(record => record.bucket === 'constipation' || record.bucket === 'loose').map(record => record.id),
+  }] : [];
+
+  return { window, records, insufficient: false, statements: [frequency, ...formLines, ...mixedLine], copy: '', boundary: BOUNDARY };
+}