disable sign-up on event day

EVENT_DATES_GUIDE.md

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+# Event Dates Management Guide
+
+## How to Block Sign-ups on Event Days
+
+The sign-up form automatically closes at 3pm on specified event dates to prevent last-minute registrations.
+
+### Managing Event Dates
+
+1. Open the `event-dates.json` file in the project root
+2. Add or remove dates in the `eventDates` array
+3. Use the format `YYYY-MM-DD` (e.g., "2024-12-25" for December 25, 2024)
+
+### Example Configuration
+
+```json
+{
+  "eventDates": ["2025-09-05", "1999-01-01"],
+  "cutoffTime": "15:00",
+  "message": "Sign-ups are closed for today's event. Please come back tomorrow."
+}
+```
+
+### Important Notes
+
+- The cutoff time is set to 3pm (15:00) by default
+- Sign-ups will automatically reopen at midnight after an event day
+- Users will see a friendly message when sign-ups are closed
+- The time zone follows the server's local time
+
+### Adding New Event Dates
+
+Simply add a new date to the array:
+
+```json
+"eventDates": [
+  "2024-12-25",
+  "2024-12-31",
+  "2025-01-15",
+  "2025-02-14",
+  "2025-03-20"  // <- New date added
+]
+```
+
+Remember to save the file after making changes!