fix(budget): name the category parking and file parking bookings in it

The key was 'parkings', which is not a word and does not match the 'parking'
the reservation type uses everywhere else. The shared trip page prints the
stored category verbatim, so a share link would have shown "parkings" in every
language.

The category also had no relationship to the booking type of the same name:
RESERVATION_TYPE_TO_COST_CATEGORY still sent a parking booking's auto-expense
to Transport, so the new bucket sat empty next to the costs that belong in it
while a manually typed "parking" resolved into it. Both paths agree now.

shared/src/budget/budget.schema.spec.ts

@@ -4,6 +4,7 @@ import {
   budgetToggleMemberPaidRequestSchema,
   budgetReorderItemsRequestSchema,
   COST_CATEGORIES,
+  typeToCostCategory,
 } from './budget.schema';
 
 import { describe, it, expect } from 'vitest';
@@ -44,8 +45,19 @@ describe('budgetReorderItemsRequestSchema', () => {
 });
 
 describe('COST_CATEGORIES', () => {
-  it('includes fuel and parkings alongside the existing fixed categories', () => {
+  it('includes fuel and parking alongside the existing fixed categories', () => {
     expect(COST_CATEGORIES).toContain('fuel');
-    expect(COST_CATEGORIES).toContain('parkings');
+    expect(COST_CATEGORIES).toContain('parking');
+  });
+});
+
+describe('typeToCostCategory', () => {
+  it('files a parking booking under parking, not transport', () => {
+    expect(typeToCostCategory('parking')).toBe('parking');
+  });
+
+  it('leaves the other vehicle types on transport', () => {
+    expect(typeToCostCategory('car-rental')).toBe('transport');
+    expect(typeToCostCategory('taxi')).toBe('transport');
   });
 });

shared/src/budget/budget.schema.ts

@@ -47,7 +47,7 @@ export const COST_CATEGORIES = [
   'health',
   'tips',
   'fuel',
-  'parkings',
+  'parking',
   'other',
 ] as const;
 export type CostCategory = (typeof COST_CATEGORIES)[number];
@@ -72,7 +72,7 @@ const RESERVATION_TYPE_TO_COST_CATEGORY: Record<string, CostCategory> = {
   hotel: 'accommodation',
   accommodation: 'accommodation',
   lodging: 'accommodation',
-  parking: 'transport',
+  parking: 'parking',
   restaurant: 'food',
   activity: 'activities',
 };