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/firmsCsv.js

@@ -153,7 +153,13 @@ export function acquisitionMsUtc(acqDate, acqTime) {
     minutes > 59
   )
     return NaN;
-  return Date.UTC(year, month - 1, day, hours, minutes);
+  const ms = Date.UTC(year, month - 1, day, hours, minutes);
+  const parsed = new Date(ms);
+  return parsed.getUTCFullYear() === year &&
+    parsed.getUTCMonth() === month - 1 &&
+    parsed.getUTCDate() === day
+    ? ms
+    : NaN;
 }
 
 /**