Decompose the remaining God Components into hooks, helpers and sub-components

FE6: split the oversized page and panel components into thin layout shells plus colocated use<Component> hooks, .constants.ts, .helpers.ts (with tests) and presentational sub-components, following the established 'logic in a hook, render in slices' pattern. Behaviour, markup, classes and effect order are unchanged. Largest reductions: PackingListPanel 1598->42, FileManager 1055->36, AdminPage 1525->167, BudgetPanel 1266->146, JourneyDetailPage 2822->547, PlacesSidebar 945->66, CollabChat 861->106, CollabNotes 1417->532. DayPlanSidebar's drag-and-drop render body was left intact (ref-identity sensitive) and only its toolbar/modals/constants were extracted.

client/src/components/Files/FileManager.helpers.ts

@@ -0,0 +1,39 @@
+import { FileText, FileImage, File, Plane, Train, Car, Ship } from 'lucide-react'
+import { downloadFile } from '../../utils/fileDownload'
+
+export function isImage(mimeType?: string | null) {
+  if (!mimeType) return false
+  return mimeType.startsWith('image/')
+}
+
+export function getFileIcon(mimeType?: string | null) {
+  if (!mimeType) return File
+  if (mimeType === 'application/pdf') return FileText
+  if (isImage(mimeType)) return FileImage
+  return File
+}
+
+export function formatSize(bytes?: number | null) {
+  if (!bytes) return ''
+  if (bytes < 1024) return `${bytes} B`
+  if (bytes < 1024 * 1024) return `${(bytes / 1024).toFixed(1)} KB`
+  return `${(bytes / 1024 / 1024).toFixed(1)} MB`
+}
+
+export function triggerDownload(url: string, filename: string) {
+  downloadFile(url, filename).catch(() => {})
+}
+
+export function formatDateWithLocale(dateStr?: string | null, locale?: string) {
+  if (!dateStr) return ''
+  try {
+    return new Date(dateStr).toLocaleDateString(locale, { day: '2-digit', month: '2-digit', year: 'numeric' })
+  } catch { return '' }
+}
+
+export function transportIcon(type: string) {
+  if (type === 'train') return Train
+  if (type === 'car') return Car
+  if (type === 'cruise') return Ship
+  return Plane
+}