feat(hunt): track walking distance via GPS, show live locations on map

Add foreground-only GPS distance tracking for hunts

app/composables/useFormatDistance.ts

@@ -0,0 +1,31 @@
+/**
+ * Locale-aware walking-distance formatting.
+ *
+ * Distances are stored as Int meters. Under 1000 m they render as whole
+ * meters, above that as kilometers with one decimal (e.g. "1.2 km"). Reused by
+ * the tracking card, the team leaderboards and the profile distances.
+ */
+export function useFormatDistance() {
+  const { locale } = useI18n();
+
+  function formatDistance(meters: number | null | undefined): string {
+    const value = meters ?? 0;
+    const loc = locale.value || 'en';
+
+    if (value < 1000) {
+      return new Intl.NumberFormat(loc, {
+        style: 'unit',
+        unit: 'meter',
+        maximumFractionDigits: 0
+      }).format(Math.round(value));
+    }
+
+    return new Intl.NumberFormat(loc, {
+      style: 'unit',
+      unit: 'kilometer',
+      maximumFractionDigits: 1
+    }).format(value / 1000);
+  }
+
+  return { formatDistance };
+}