fix: use local time with 3am cutover for today's date

new Date().toISOString() returns UTC, causing the calendar to advance
to the next day at 8pm EDT / 7pm EST. getTodayLocal() reads local
wall-clock time and rolls back one day before 3am so the calendar
stays on the current day through the night.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

lib/env.ts

@@ -11,3 +11,25 @@ export function parseStalenessHours(envVar: string | undefined, defaultHours: nu
   const parsed = parseInt(envVar ?? "", 10);
   return Number.isFinite(parsed) && parsed > 0 ? parsed : defaultHours;
 }
+
+/**
+ * Returns today's date as YYYY-MM-DD using local wall-clock time with a 3 AM
+ * switchover. Before 3 AM local time we still consider it "yesterday", so the
+ * calendar doesn't flip to the next day at midnight while people are still out
+ * at the park.
+ *
+ * Important: `new Date().toISOString()` returns UTC, which causes the date to
+ * advance at 8 PM EDT (UTC-4) or 7 PM EST (UTC-5) — too early. This helper
+ * corrects that by using local year/month/day components and rolling back one
+ * day when the local hour is before 3.
+ */
+export function getTodayLocal(): string {
+  const now = new Date();
+  if (now.getHours() < 3) {
+    now.setDate(now.getDate() - 1);
+  }
+  const y = now.getFullYear();
+  const m = String(now.getMonth() + 1).padStart(2, "0");
+  const d = String(now.getDate()).padStart(2, "0");
+  return `${y}-${m}-${d}`;
+}