feat(dashboard): add pre-copy confirmation modal showing what will and won't be copied

Introduces CopyTripDialog — a two-section modal that appears before the
copy action and lists what is carried over (days, places, budget items,
packing lists, TODOs, notes) and what is intentionally skipped
(collaborators, collab data, files, share tokens). Addresses the UX gap
raised in #786.

client/src/i18n/translations/en.ts

@@ -122,6 +122,20 @@ const en: Record<string, string | { name: string; category: string }[]> = {
   'dashboard.toast.copied': 'Trip copied!',
   'dashboard.toast.copyError': 'Failed to copy trip',
   'dashboard.confirm.delete': 'Delete trip "{title}"? All places and plans will be permanently deleted.',
+  'dashboard.confirm.copy.title': 'Copy this trip?',
+  'dashboard.confirm.copy.willCopy': 'Will be copied',
+  'dashboard.confirm.copy.will1': 'Days, places & day assignments',
+  'dashboard.confirm.copy.will2': 'Accommodations & reservations',
+  'dashboard.confirm.copy.will3': 'Budget items & category order',
+  'dashboard.confirm.copy.will4': 'Packing lists (unchecked)',
+  'dashboard.confirm.copy.will5': 'TODOs (unassigned & unchecked)',
+  'dashboard.confirm.copy.will6': 'Day notes',
+  'dashboard.confirm.copy.wontCopy': "Won't be copied",
+  'dashboard.confirm.copy.wont1': 'Collaborators & member assignments',
+  'dashboard.confirm.copy.wont2': 'Collab notes, polls & messages',
+  'dashboard.confirm.copy.wont3': 'Files & photos',
+  'dashboard.confirm.copy.wont4': 'Share tokens',
+  'dashboard.confirm.copy.confirm': 'Copy trip',
   'dashboard.editTrip': 'Edit Trip',
   'dashboard.createTrip': 'Create New Trip',
   'dashboard.tripTitle': 'Title',