feat(dashboard): add date difference and timezone conversion tools for dashboard

src/lib/utils/dates.ts

@@ -0,0 +1,52 @@
+import { DateTime } from 'luxon';
+
+/**
+ * Parses a date string using multiple Luxon formats with fallback to JavaScript Date parsing.
+ * Preserves timezone information when available using setZone: true.
+ * 
+ * @param dateString - The date string to parse
+ * @returns A parsed DateTime object
+ */
+export function parseDate(dateString: string): DateTime {
+  // Try to parse as ISO format first (most common)
+  let dateTime = DateTime.fromISO(dateString, { setZone: true });
+  
+  // If ISO parsing fails, try other common formats
+  if (!dateTime.isValid) {
+    dateTime = DateTime.fromRFC2822(dateString, { setZone: true });
+  }
+  
+  if (!dateTime.isValid) {
+    dateTime = DateTime.fromHTTP(dateString, { setZone: true });
+  }
+  
+  if (!dateTime.isValid) {
+    dateTime = DateTime.fromSQL(dateString, { setZone: true });
+  }
+  
+  // If all parsing attempts fail, try JavaScript Date parsing as fallback
+  if (!dateTime.isValid) {
+    const jsDate = new Date(dateString);
+    if (!isNaN(jsDate.getTime())) {
+      dateTime = DateTime.fromJSDate(jsDate);
+    }
+  }
+  
+  return dateTime;
+}
+
+/**
+ * Generates a standardized error message for date parsing failures.
+ * 
+ * @param dateString - The original date string that failed to parse
+ * @param dateTime - The invalid DateTime object
+ * @param fieldName - Optional field name for more specific error messages (e.g., "start date", "end date")
+ * @returns A formatted error message
+ */
+export function getDateParseErrorMessage(
+  dateString: string, 
+  dateTime: DateTime, 
+  fieldName: string = 'date'
+): string {
+  return `Error: Unable to parse ${fieldName} "${dateString}". Please provide a valid date format (ISO 8601, RFC 2822, SQL, or common date formats). Reason: ${dateTime.invalidReason}`;
+}