fix: use park timezone for operating window check; show tz in hours

- isWithinOperatingWindow now accepts an IANA timezone and reads the
  current time in the park's local timezone via Intl.DateTimeFormat,
  fixing false positives when the server runs in UTC but parks store
  hours in local time (e.g. Pacific parks showing open at 6:50 AM EDT)
- Remove the 1-hour pre-open buffer so parks are not marked open before
  their doors actually open; retain the 1-hour post-close grace period
- Add getTimezoneAbbr() helper to derive the short tz label (EDT, PDT…)
- All hours labels now display with the local timezone abbreviation
  (e.g. "10am – 6pm PDT") in WeekCalendar, ParkCard, and ParkMonthCalendar

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

components/ParkMonthCalendar.tsx

@@ -1,5 +1,6 @@
 import Link from "next/link";
 import type { DayData } from "@/lib/db";
+import { getTimezoneAbbr } from "@/lib/env";
 
 interface ParkMonthCalendarProps {
   parkId: string;
@@ -7,6 +8,7 @@ interface ParkMonthCalendarProps {
   month: number; // 1-indexed
   monthData: Record<string, DayData>; // 'YYYY-MM-DD' → DayData
   today: string; // YYYY-MM-DD
+  timezone: string; // IANA timezone, e.g. "America/New_York"
 }
 
 const DOW_LABELS = ["Sun", "Mon", "Tue", "Wed", "Thu", "Fri", "Sat"];
@@ -29,7 +31,8 @@ function daysInMonth(year: number, month: number): number {
   return new Date(year, month, 0).getDate();
 }
 
-export function ParkMonthCalendar({ parkId, year, month, monthData, today }: ParkMonthCalendarProps) {
+export function ParkMonthCalendar({ parkId, year, month, monthData, today, timezone }: ParkMonthCalendarProps) {
+  const tzAbbr = getTimezoneAbbr(timezone);
   const firstDow = new Date(year, month - 1, 1).getDay(); // 0=Sun
   const totalDays = daysInMonth(year, month);
 
@@ -184,7 +187,7 @@ export function ParkMonthCalendar({ parkId, year, month, monthData, today }: Par
                         Passholder
                       </div>
                       <div style={{ fontSize: "0.65rem", color: "var(--color-ph-hours)", marginTop: 2 }}>
-                        {dayData.hoursLabel}
+                        {dayData.hoursLabel} {tzAbbr}
                       </div>
                     </div>
                   ) : isOpen ? (
@@ -195,7 +198,7 @@ export function ParkMonthCalendar({ parkId, year, month, monthData, today }: Par
                       padding: "3px 6px",
                     }}>
                       <div style={{ fontSize: "0.65rem", color: "var(--color-open-hours)" }}>
-                        {dayData.hoursLabel}
+                        {dayData.hoursLabel} {tzAbbr}
                       </div>
                     </div>
                   ) : (