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/components/Budget/BudgetPanel.tsx

@@ -633,7 +633,7 @@ export default function BudgetPanel({ tripId, tripMembers = [] }: BudgetPanelPro
                             onMouseEnter={e => e.currentTarget.style.background = 'var(--bg-hover)'}
                             onMouseLeave={e => e.currentTarget.style.background = 'transparent'}>
                             <td style={td}>
-                              <InlineEditCell value={item.name} onSave={v => handleUpdateField(item.id, 'name', v)} placeholder={t('budget.table.name')} locale={locale} editTooltip={t('budget.editTooltip')} readOnly={!canEdit} />
+                              <InlineEditCell value={item.name} onSave={v => handleUpdateField(item.id, 'name', v)} placeholder={t('budget.table.name')} locale={locale} editTooltip={item.reservation_id ? t('budget.linkedToReservation') : t('budget.editTooltip')} readOnly={!canEdit || !!item.reservation_id} />
                               {/* Mobile: larger chips under name since Persons column is hidden */}
                               {hasMultipleMembers && (
                                 <div className="sm:hidden" style={{ marginTop: 4 }}>

client/src/components/Planner/ReservationModal.tsx

@@ -207,13 +207,10 @@ export function ReservationModal({ isOpen, onClose, onSave, reservation, days, p
         accommodation_id: form.type === 'hotel' ? (form.accommodation_id || null) : null,
         metadata: Object.keys(metadata).length > 0 ? metadata : null,
       }
-      // Auto-create budget entry if price is set
-      if (form.price && parseFloat(form.price) > 0) {
-        saveData.create_budget_entry = {
-          total_price: parseFloat(form.price),
-          category: form.budget_category || t(`reservations.type.${form.type}`) || 'Other',
-        }
-      }
+      // Auto-create/update budget entry if price is set, or signal removal if cleared
+      saveData.create_budget_entry = form.price && parseFloat(form.price) > 0
+        ? { total_price: parseFloat(form.price), category: form.budget_category || t(`reservations.type.${form.type}`) || 'Other' }
+        : { total_price: 0 }
       // If hotel with place + days, pass hotel data for auto-creation or update
       if (form.type === 'hotel' && form.hotel_place_id && form.hotel_start_day && form.hotel_end_day) {
         saveData.create_accommodation = {

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',

client/src/store/slices/budgetSlice.ts

@@ -42,6 +42,9 @@ export const createBudgetSlice = (set: SetState, get: GetState): BudgetSlice =>
       set(state => ({
         budgetItems: state.budgetItems.map(item => item.id === id ? result.item : item)
       }))
+      if (result.item.reservation_id && data.total_price !== undefined) {
+        get().loadReservations(tripId)
+      }
       return result.item
     } catch (err: unknown) {
       throw new Error(getApiErrorMessage(err, 'Error updating budget item'))