feat(pure): summary with today/week counts and per-day rate

tests/pure.test.js

@@ -1,6 +1,6 @@
 import { test } from 'node:test';
 import assert from 'node:assert/strict';
-import { parseTarget, computeEstimate, pruneHistory, MS_PER_DAY } from '../src/pure.js';
+import { parseTarget, computeEstimate, pruneHistory, summary, MS_PER_DAY } from '../src/pure.js';
 
 const DAY = MS_PER_DAY;
 const NOW = 1_700_000_000_000; // fixed reference
@@ -94,3 +94,48 @@ test('pruneHistory: does not mutate input', () => {
 test('pruneHistory: empty input', () => {
   assert.deepEqual(pruneHistory([], NOW), []);
 });
+
+test('summary: empty history returns zeros', () => {
+  const s = summary([], NOW);
+  assert.equal(s.trainsToday, 0);
+  assert.equal(s.sevenDayAvgPerDay, 0);
+  assert.equal(s.perDay, 0);
+});
+
+test('summary: counts trains within last 24h', () => {
+  const entries = [
+    { ts: NOW - 1 * 60_000, delta: 100 },   // 1 min ago
+    { ts: NOW - 12 * 3_600_000, delta: 100 }, // 12h ago
+    { ts: NOW - 23 * 3_600_000, delta: 100 }, // 23h ago
+    { ts: NOW - 25 * 3_600_000, delta: 100 }, // 25h ago (not today)
+  ];
+  const s = summary(entries, NOW);
+  assert.equal(s.trainsToday, 3);
+});
+
+test('summary: 7-day average is total/7', () => {
+  // 14 entries in last 7 days (spaced 12h apart, all within window)
+  const entries = [];
+  for (let i = 0; i < 14; i++) {
+    entries.push({ ts: NOW - (i / 2) * DAY, delta: 100 });
+  }
+  const s = summary(entries, NOW);
+  assert.equal(s.sevenDayAvgPerDay, 2);
+});
+
+test('summary: perDay uses most recent delta when available', () => {
+  const entries = [
+    { ts: NOW - 1 * 60_000, delta: 247 },
+    { ts: NOW - 12 * 3_600_000, delta: 300 },
+  ];
+  const s = summary(entries, NOW);
+  // 2 trains in last 7 days → 2/7 avg
+  // perDay = avg * most recent delta = (2/7) * 247 = ~70.57
+  assert.equal(s.perDay, Math.floor((2 / 7) * 247));
+});
+
+test('summary: perDay is 0 when no recent delta', () => {
+  const entries = [{ ts: NOW - 31 * DAY, delta: 100 }];
+  const s = summary(entries, NOW);
+  assert.equal(s.perDay, 0);
+});