feat: festival/series model with sub-events, cross-event sections, tab navigation, SectionsShiftsPanel extraction

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/app/src/stores/useSectionsUiStore.ts

@@ -0,0 +1,20 @@
+import { defineStore } from 'pinia'
+import { ref } from 'vue'
+
+export const useSectionsUiStore = defineStore('sectionsUi', () => {
+  const timeSlotsExpanded = ref(false)
+
+  function toggleTimeSlots() {
+    timeSlotsExpanded.value = !timeSlotsExpanded.value
+  }
+
+  function expandTimeSlots() {
+    timeSlotsExpanded.value = true
+  }
+
+  return {
+    timeSlotsExpanded,
+    toggleTimeSlots,
+    expandTimeSlots,
+  }
+})