feat(algo): slotsPerDay parameter for top-N selection

tests/algorithm.test.mjs

@@ -121,4 +121,37 @@ function emp(id, constraints = {}) {
   assert.equal(result.assignments[0].manual, false, 'auto-assignment sets manual: false');
 }
 
+// slotsPerDay=2 → 2 different employees per day
+{
+  const employees = [emp('alice'), emp('bob'), emp('clara')];
+  const result = generatePlan(['2026-04-01'], employees, [], fixed, 2);
+  assert.equal(result.assignments.length, 2, 'slotsPerDay=2 → 2 entries');
+  const ids = result.assignments.map(a => a.employeeId);
+  assert.notEqual(ids[0], ids[1], 'two different employees on same day');
+}
+
+// slotsPerDay=2 across multiple days, maxPerMonth still respected
+{
+  const days = ['2026-04-01','2026-04-02','2026-04-03'];
+  const employees = [
+    emp('alice', { maxPerMonth: 1 }),
+    emp('bob'),
+    emp('clara'),
+    emp('dave')
+  ];
+  const result = generatePlan(days, employees, [], fixed, 2);
+  const aliceCount = result.assignments.filter(a => a.employeeId === 'alice').length;
+  assert.ok(aliceCount <= 1, 'maxPerMonth=1 respected with slotsPerDay=2');
+}
+
+// slotsPerDay=2: per day, no employee picked twice
+{
+  const employees = [emp('alice'), emp('bob'), emp('clara')];
+  const result = generatePlan(['2026-04-01','2026-04-02'], employees, [], fixed, 2);
+  for (const date of ['2026-04-01','2026-04-02']) {
+    const ids = result.assignments.filter(a => a.date === date).map(a => a.employeeId);
+    assert.equal(new Set(ids).size, ids.length, 'no employee picked twice on ' + date);
+  }
+}
+
 console.log('All algorithm tests passed.');