fix(i18n): every language says one file and five files its own way

Finishes the plural work the previous wip commit started. t() picks a
count string's form by the language's own Intl.PluralRules, and every
locale now spells out the forms its language reaches with whole
numbers, about 160 count strings in all: one, few and many in Russian,
Ukrainian and Polish, one and few in Czech and Slovak, five forms in
Arabic, one in the others, none in Japanese, Korean, Chinese, Thai,
Vietnamese and Indonesian. Each language was translated and then
reviewed on its own. English no longer reads "1 files", "1 updates
available" or "photo(s)".

Count labels shown next to a number now take that number too: the
atlas and admin statistics, the trip cards, journey and shared trip
pills, packing templates, receipts, storage usage, the Studio export
note. A heading that shared its key with a counted label keeps a key of
its own (the boarding pass heading, the Bookings tab), so languages that
put a noun after a number in the singular keep a plural heading. The
plugin hosts chip passed its count through .replace() after t() and
never got a form; three toasts sent the count as text. Mail and push
texts for shared photos and suppressed storage failures pick their form
in code through pluralForm.

A whole number sent as text counts too, which is how in-app
notification params arrive, and the plural rule follows the language of
the strings on screen while another one still loads.

The parity check knows which forms each language needs and refuses
missing and impossible ones. It also reads keys that contain a colon
now: it skipped them, which hid 58 missing plugin permission texts in
Catalan and 35 in Vietnamese, both translated. The client parity test
covers every language of the registry instead of a hand-kept list of 19,
and the placeholder spec lets a form spell its number out only where
its category is that one number. Brazilian Portuguese error screens
were in Breton, and an Arabic dashboard label held Hebrew text.

client/src/components/Planner/DayPlanSidebar.test.tsx

@@ -527,7 +527,7 @@ describe('DayPlanSidebar', () => {
     // title uses an arrow icon, so its parts are separate text nodes.
     expect(screen.getByText('U2')).toBeInTheDocument()
     // Transfer counts stay out of the compact row — the chips say it all.
-    expect(screen.queryByText(/1 transfers/)).not.toBeInTheDocument()
+    expect(screen.queryByText(/1 transfer/)).not.toBeInTheDocument()
     // Clicking the row opens the journey view — not the edit form.
     await user.click(screen.getByText('Fernsehturm'))
     expect(onEditTransport).not.toHaveBeenCalled()

client/src/components/Planner/PlaceInspector.test.tsx

@@ -1119,7 +1119,7 @@ describe('PlaceInspector', () => {
     const { openFile } = await import('../../utils/fileDownload');
     const spy = vi.spyOn({ openFile }, 'openFile');
     render(<PlaceInspector {...defaultProps} files={[placeFile()] as any} />);
-    fireEvent.click(screen.getByText('1 files'));
+    fireEvent.click(screen.getByText('1 file'));
     const link = await screen.findByText('map.pdf');
     fireEvent.click(link);
     // The click is handled without throwing; the row stays in the list.

client/src/components/Planner/PlacesSidebarHeader.tsx

@@ -262,7 +262,7 @@ function CategoryFilter(S: SidebarState) {
     if (categoryFilters.has(UNCATEGORIZED)) label = t('places.noCategory')
     else if (only) label = only.name
   } else if (categoryFilters.size > 1) {
-    label = `${categoryFilters.size} ${t('places.categoriesSelected')}`
+    label = `${categoryFilters.size} ${t('places.categoriesSelected', { count: categoryFilters.size })}`
   }
   return (
     <FilterDropdown name={t('categories.title')} label={label} active={categoryFilters.size > 0} badge={categoryFilters.size}

client/src/components/Planner/TransitSearchPanel.test.tsx

@@ -107,7 +107,7 @@ describe('TransitSearchPanel', () => {
     // Local Berlin times, U2 badge, 1 transfer.
     expect(await screen.findByText(/08:30 – 09:00/)).toBeInTheDocument()
     expect(screen.getByText('U2')).toBeInTheDocument()
-    expect(screen.getByText('1 transfers')).toBeInTheDocument()
+    expect(screen.getByText('1 transfer')).toBeInTheDocument()
   })
 
   it('FE-PLANNER-TRANSIT-003: adding a route builds a transport payload with local times + endpoints', async () => {

client/src/components/Planner/usePlacesSidebar.test.tsx

@@ -611,7 +611,7 @@ describe('usePlacesSidebar list import', () => {
     await act(async () => { await S.handleListImport(); });
 
     expect(sentEnrich).toBe(true);
-    expect(addToast).toHaveBeenCalledWith('1 places imported from "Seoul"', 'success', undefined);
+    expect(addToast).toHaveBeenCalledWith('1 place imported from "Seoul"', 'success', undefined);
     expect(pushUndo).toHaveBeenCalledWith('Naver Maps import', expect.any(Function));
   });