Fix timezone display: parse UTC timestamps correctly in logs pages

Agent-Logs-Url: https://github.com/christianlouis/InboxConverge/sessions/70a69601-e0b9-4a00-bcf4-0a85d2bdf6cb

Co-authored-by: christianlouis <361235+christianlouis@users.noreply.github.com>

frontend/src/lib/date-utils.ts

@@ -0,0 +1,16 @@
+/**
+ * Parse an ISO-8601 datetime string as UTC.
+ *
+ * The backend stores all timestamps in UTC.  When the serialised string has no
+ * explicit timezone indicator (no trailing `Z` or `±HH:MM` offset), JavaScript's
+ * `Date` constructor treats it as *local* time.  For clients in UTC+N this
+ * shifts every timestamp N hours into the past, causing "Xh ago" relative
+ * labels and `toLocaleString()` absolute dates to be wrong.
+ *
+ * This helper appends `Z` to any timezone-naive ISO string so it is always
+ * interpreted as UTC.  Strings that already carry timezone info are passed
+ * through unchanged.
+ */
+export function parseUTC(iso: string): Date {
+  return new Date(/Z|[+-]\d{2}:?\d{2}$/.test(iso) ? iso : iso + 'Z');
+}