refactor(planner): the day plan's drag state lives in a hook of its own; the holiday provider cases get a suite of their own

DayPlanSidebar grew past its size baseline with the Firefox drag fix. Its drag state (what is dragged, the drop line, the day under the drag, whether a drag happened) and the effect that ends a lost drag move into useDayPlanDragState, typed, which also lowers the file's strict-mode count; size and strict baselines are lowered with it.

vacay.service.test.ts went past the 2000-line limit once the Nager v4 cases were back in it. They move into vacay.holiday-provider.test.ts, which takes VacayService from a Nest testing module over a snapshot db, so neither the db mock nor a hand-built service is needed.

client/scripts/size-baseline.json

@@ -10,7 +10,7 @@
   "src/components/Map/MapViewGL.tsx": 2126,
   "src/components/Planner/DayDetailPanel.test.tsx": 2333,
   "src/components/Planner/DayPlanSidebar.test.tsx": 5349,
-  "src/components/Planner/DayPlanSidebar.tsx": 2929,
+  "src/components/Planner/DayPlanSidebar.tsx": 2910,
   "src/components/Planner/PlaceFormModal.test.tsx": 2836,
   "src/components/Planner/PlaceInspector.tsx": 1287,
   "src/components/Studio/TravelElements.tsx": 1559,

client/scripts/strict-baseline.json

@@ -46,7 +46,7 @@
   "src/components/PDF/TripPDF.tsx": 40,
   "src/components/Packing/PackingListPanelItemRow.test.tsx": 2,
   "src/components/Planner/DayPlanSidebar.constants.ts": 1,
-  "src/components/Planner/DayPlanSidebar.tsx": 61,
+  "src/components/Planner/DayPlanSidebar.tsx": 52,
   "src/components/Planner/DayPlanSidebarNoteModal.test.tsx": 1,
   "src/components/Planner/PlaceFormModal.test.tsx": 3,
   "src/components/Planner/PlaceFormModal.tsx": 1,