feat(budget): bidirectional sync between reservations and budget items

- Link budget items to reservations via reservation_id column
- Update budget entry when reservation price changes (not create duplicate)
- Delete budget entry when reservation price is cleared
- Sync price back to reservation when edited in budget panel
- Lock budget item name when linked to a reservation
- Add migration 73 for reservation_id on budget_items

client/src/i18n/translations/de.ts

@@ -1005,6 +1005,7 @@ const de: Record<string, string | { name: string; category: string }[]> = {
   'budget.totalBudget': 'Gesamtbudget',
   'budget.byCategory': 'Nach Kategorie',
   'budget.editTooltip': 'Klicken zum Bearbeiten',
+  'budget.linkedToReservation': 'Verknüpft mit einer Buchung — Name dort bearbeiten',
   'budget.confirm.deleteCategory': 'Möchtest du die Kategorie "{name}" mit {count} Einträgen wirklich löschen?',
   'budget.deleteCategory': 'Kategorie löschen',
   'budget.perPerson': 'Pro Person',

client/src/i18n/translations/en.ts

@@ -1024,6 +1024,7 @@ const en: Record<string, string | { name: string; category: string }[]> = {
   'budget.totalBudget': 'Total Budget',
   'budget.byCategory': 'By Category',
   'budget.editTooltip': 'Click to edit',
+  'budget.linkedToReservation': 'Linked to a reservation — edit the name there',
   'budget.confirm.deleteCategory': 'Are you sure you want to delete the category "{name}" with {count} entries?',
   'budget.deleteCategory': 'Delete Category',
   'budget.perPerson': 'Per Person',