Reorder whole days and insert a day (#589) (#1148)

* feat(days): reorder whole days and insert a day at a position

Adds reorderDays + insertDay to the day service and a PUT /days/reorder route
(plus an optional position on create). Day rows stay stable so a day's
assignments, notes, bookings and accommodations ride along by id; on a dated
trip the calendar dates stay pinned to their slots while the content moves
across them, and each booking's date is re-stamped onto its day's new date
(time-of-day preserved) so day_id stays consistent. Renumbering uses the
two-phase write to avoid the UNIQUE(trip_id, day_number) collision, and a move
that would invert an accommodation's check-in/out span is rejected.

* feat(planner): reorder days from a toolbar popup, and add days

A new toolbar button opens a popup listing the days; drag a row by its grip or
use the up/down arrows to reorder, and add a day from there. Reorders apply
optimistically with rollback and sync over WebSocket; the day headers are left
untouched, so the existing place drop-targets are unaffected.

* i18n: add day-reorder strings across all languages

shared/src/i18n/de/dayplan.ts

@@ -47,5 +47,14 @@ const dayplan: TranslationStrings = {
   'dayplan.mobile.allAssigned': 'Alle Orte zugeordnet',
   'dayplan.mobile.noMatch': 'Kein Treffer',
   'dayplan.mobile.createNew': 'Neuen Ort erstellen',
+  'dayplan.reorderDays': 'Tage neu anordnen',
+  'dayplan.reorderTitle': 'Tage neu anordnen',
+  'dayplan.reorderHint': 'Orte, Notizen und Buchungen eines Tages werden mitverschoben.',
+  'dayplan.addDay': 'Tag hinzufügen',
+  'dayplan.moveUp': 'Nach oben',
+  'dayplan.moveDown': 'Nach unten',
+  'dayplan.reorderUndo': 'Tage neu anordnen',
+  'dayplan.reorderError': 'Tage konnten nicht neu angeordnet werden',
+  'dayplan.addDayError': 'Tag konnte nicht hinzugefügt werden',
 };
 export default dayplan;