fix(firms): reject impossible acquisition days in CSV parsing

Rebased onto current main with review follow-ups folded in.

Co-Authored-By: Claude Sonnet 5.5 <[email protected]>

src/data/firms-calendar-validity.test.mjs

@@ -0,0 +1,23 @@
+import test from 'node:test';
+import assert from 'node:assert/strict';
+import { acquisitionMsUtc } from './firmsCsv.js';
+test('FIRMS acquisition dates cannot roll into a different calendar day', () => {
+  for (const [date, time] of [
+    ['2026-02-30', '1200'],
+    ['2026-04-31', '1200'],
+    ['2026-13-01', '1200'],
+    ['2026-07-16junk', '1200'],
+    ['2026-07-16', '2400'],
+    ['2026-07-16', '1260'],
+    ['2026-07-16', null],
+    ['2026-07-16', ''],
+  ]) {
+    assert.ok(Number.isNaN(acquisitionMsUtc(date, time)), `${date}:${time}`);
+  }
+  for (const [date, time, expected] of [
+    ['2024-02-29', '45', Date.UTC(2024, 1, 29, 0, 45)],
+    ['2026-07-16', '0', Date.UTC(2026, 6, 16)],
+  ]) {
+    assert.equal(acquisitionMsUtc(date, time), expected);
+  }
+});