i18n: counts follow the OS region instead of always en-US

`formatNumber` and the loading-overlay count now group thousands by the active locale (via the `lib/intl` chokepoint), so a German-region user sees `1.234` where the hardcoded en-US path showed `1,234`. This is the native-correct behavior and aligns counts with the dates that already localize. An en-US-region runtime is unchanged (parity net stays green).

- `formatNumber` delegates to `formatInteger` (memoized locale formatter); the `'en-US'` literal is gone.
- `LoadingIcon.svelte` routes through the same helper instead of a bare `toLocaleString()` (it previously used the runtime default, inconsistent with the rest of the app).

Author: vdavid

apps/desktop/src/lib/file-explorer/selection/selection-info-utils.test.ts

@@ -1,7 +1,7 @@
 /**
  * Tests for selection-info-utils.ts
  */
-import { describe, it, expect } from 'vitest'
+import { afterEach, describe, it, expect } from 'vitest'
 import {
   formatSizeTriads,
   formatSizeForDisplay,
@@ -17,6 +17,7 @@ import {
   calculatePercentage,
 } from './selection-info-utils'
 import { formatDateForDisplay } from '$lib/settings/format-utils'
+import { _setLocaleForTests } from '$lib/intl/locale'
 import type { FileEntry } from '../types'
 
 // Helper to create a basic file entry
@@ -459,26 +460,39 @@ describe('formatSizeForDisplay', () => {
 // ============================================================================
 
 describe('formatNumber', () => {
+  afterEach(() => {
+    _setLocaleForTests(null)
+  })
+
   it('formats small numbers without separators', () => {
     expect(formatNumber(0)).toBe('0')
     expect(formatNumber(1)).toBe('1')
     expect(formatNumber(999)).toBe('999')
   })
 
-  it('formats thousands with comma separator', () => {
+  it('formats thousands with comma separator (en-US)', () => {
+    _setLocaleForTests('en-US')
     expect(formatNumber(1000)).toBe('1,000')
     expect(formatNumber(1234)).toBe('1,234')
     expect(formatNumber(9999)).toBe('9,999')
   })
 
-  it('formats millions with multiple comma separators', () => {
+  it('formats millions with multiple comma separators (en-US)', () => {
+    _setLocaleForTests('en-US')
     expect(formatNumber(1000000)).toBe('1,000,000')
     expect(formatNumber(1234567)).toBe('1,234,567')
   })
 
-  it('formats large numbers correctly', () => {
+  it('formats large numbers correctly (en-US)', () => {
+    _setLocaleForTests('en-US')
     expect(formatNumber(1234567890)).toBe('1,234,567,890')
   })
+
+  it('follows the active locale: de-DE groups with a period', () => {
+    _setLocaleForTests('de-DE')
+    expect(formatNumber(1000)).toBe('1.000')
+    expect(formatNumber(1234567)).toBe('1.234.567')
+  })
 })
 
 describe('calculatePercentage', () => {

apps/desktop/src/lib/file-explorer/selection/selection-info-utils.ts

@@ -12,6 +12,7 @@ import {
   type DateSegment,
   type FormattedDate,
 } from '$lib/settings/format-utils'
+import { formatInteger } from '$lib/intl/number-format'
 
 // Size tier colors for digit triads (indexed: 0=bytes, 1=kB, 2=MB, 3=GB, 4=TB+)
 export const sizeTierClasses = ['size-bytes', 'size-kb', 'size-mb', 'size-gb', 'size-tb']
@@ -206,9 +207,9 @@ export function isPermissionDenied(entry: FileEntry | null): boolean {
 // Selection summary utilities
 // ============================================================================
 
-/** Formats a number with thousands separators using en-US locale */
+/** Formats a count with the active locale's thousands grouping (en-US `1,234`, de-DE `1.234`). */
 export function formatNumber(n: number): string {
-  return n.toLocaleString('en-US')
+  return formatInteger(n)
 }
 
 /** Calculates percentage, rounded to nearest integer */

apps/desktop/src/lib/ui/LoadingIcon.svelte

@@ -1,6 +1,7 @@
 <script lang="ts">
     import ShortcutChip from '$lib/ui/ShortcutChip.svelte'
     import Spinner from '$lib/ui/Spinner.svelte'
+    import { formatInteger } from '$lib/intl/number-format'
 
     interface Props {
         openingFolder?: boolean
@@ -11,9 +12,7 @@
 
     const { openingFolder = false, loadedCount, finalizingCount, showCancelHint = false }: Props = $props()
 
-    function formatNumber(n: number): string {
-        return n.toLocaleString()
-    }
+    const formatNumber = formatInteger
 </script>
 
 <div class="loading-container">