polish: clarify parks open badge; improve timezone display

- "parks open" → "parks open this week" for clarity
- Week calendar cells: stack hours above tz abbreviation (smaller,
  dimmer) instead of inline to avoid overflow in tight 130px columns
- Mobile park cards: tz abbreviation inline but smaller/dimmer (60% opacity)
- Month calendar: same two-line stacking in compact day cells

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

components/WeekCalendar.tsx

@@ -100,7 +100,15 @@ function DayCell({
             letterSpacing: "-0.01em",
             whiteSpace: "nowrap",
           }}>
-            {dayData.hoursLabel} {tzAbbr}
+            {dayData.hoursLabel}
+          </span>
+          <span style={{
+            color: "var(--color-ph-label)",
+            fontSize: "0.6rem",
+            fontWeight: 500,
+            letterSpacing: "0.04em",
+          }}>
+            {tzAbbr}
           </span>
         </div>
       </td>
@@ -113,12 +121,14 @@ function DayCell({
         background: "var(--color-open-bg)",
         border: "1px solid var(--color-open-border)",
         borderRadius: 6,
-        padding: "6px 4px",
+        padding: "4px",
         textAlign: "center",
         height: "100%",
         display: "flex",
+        flexDirection: "column",
         alignItems: "center",
         justifyContent: "center",
+        gap: 2,
         transition: "filter 150ms ease",
       }}>
         <span style={{
@@ -128,7 +138,16 @@ function DayCell({
           letterSpacing: "-0.01em",
           whiteSpace: "nowrap",
         }}>
-          {dayData.hoursLabel} {tzAbbr}
+          {dayData.hoursLabel}
+        </span>
+        <span style={{
+          color: "var(--color-open-hours)",
+          fontSize: "0.6rem",
+          fontWeight: 500,
+          opacity: 0.6,
+          letterSpacing: "0.04em",
+        }}>
+          {tzAbbr}
         </span>
       </div>
     </td>