Add $lib/stores/dateStore.ts to store date in localStorage

src/lib/stores/dateStore.ts

@@ -0,0 +1,18 @@
+import { writable } from 'svelte/store';
+
+function createDateStore() {
+  const storedDate = typeof localStorage !== 'undefined' ? localStorage.getItem('selectedDate') : null;
+  const initialDate = storedDate ? storedDate : new Date().toISOString().split('T')[0];
+
+  const { subscribe, set } = writable(initialDate);
+
+  return {
+    subscribe,
+    set: (newDate: string) => {
+      localStorage.setItem('selectedDate', newDate);
+      set(newDate);
+    }
+  };
+}
+
+export const selectedDate = createDateStore();