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/pages/DashboardPage.test.tsx

@@ -401,6 +401,10 @@ describe('DashboardPage', () => {
       const copyButtons = screen.getAllByRole('button', { name: /copy/i });
       await user.click(copyButtons[0]);
 
+      // Confirm the copy dialog
+      const confirmButton = await screen.findByRole('button', { name: /copy trip/i });
+      await user.click(confirmButton);
+
       await waitFor(() => {
         expect(screen.getAllByText('Paris Adventure (Copy)')[0]).toBeInTheDocument();
       });
@@ -766,6 +770,10 @@ describe('DashboardPage', () => {
       expect(copyButtons.length).toBeGreaterThan(0);
       await user.click(copyButtons[0]);
 
+      // Confirm the copy dialog
+      const confirmButton = await screen.findByRole('button', { name: /copy trip/i });
+      await user.click(confirmButton);
+
       await waitFor(() => {
         expect(screen.getAllByText('Paris Adventure (Copy)').length).toBeGreaterThan(0);
       });

client/src/pages/DashboardPage.tsx

@@ -12,6 +12,7 @@ import CurrencyWidget from '../components/Dashboard/CurrencyWidget'
 import TimezoneWidget from '../components/Dashboard/TimezoneWidget'
 import TripFormModal from '../components/Trips/TripFormModal'
 import ConfirmDialog from '../components/shared/ConfirmDialog'
+import CopyTripDialog from '../components/shared/CopyTripDialog'
 import { useToast } from '../components/shared/Toast'
 import { useCountUp } from '../hooks/useCountUp'
 import {
@@ -699,6 +700,7 @@ export default function DashboardPage(): React.ReactElement {
   const [showWidgetSettings, setShowWidgetSettings] = useState<boolean | 'mobile' | 'mobile-currency' | 'mobile-timezone'>(false)
   const [viewMode, setViewMode] = useState<'grid' | 'list'>(() => (localStorage.getItem('trek_dashboard_view') as 'grid' | 'list') || 'grid')
   const [deleteTrip, setDeleteTrip] = useState<DashboardTrip | null>(null)
+  const [copyTrip, setCopyTrip] = useState<DashboardTrip | null>(null)
 
   const toggleViewMode = () => {
     setViewMode(prev => {
@@ -815,14 +817,18 @@ export default function DashboardPage(): React.ReactElement {
     setArchivedTrips(prev => prev.map(update))
   }
 
-  const handleCopy = async (trip: DashboardTrip) => {
+  const handleCopy = (trip: DashboardTrip) => setCopyTrip(trip)
+
+  const confirmCopy = async () => {
+    if (!copyTrip) return
     try {
-      const data = await tripsApi.copy(trip.id, { title: `${trip.title} (${t('dashboard.copySuffix')})` })
+      const data = await tripsApi.copy(copyTrip.id, { title: `${copyTrip.title} (${t('dashboard.copySuffix')})` })
       setTrips(prev => sortTrips([data.trip, ...prev]))
       toast.success(t('dashboard.toast.copied'))
     } catch {
       toast.error(t('dashboard.toast.copyError'))
     }
+    setCopyTrip(null)
   }
 
   const today = new Date().toISOString().split('T')[0]
@@ -1205,6 +1211,13 @@ export default function DashboardPage(): React.ReactElement {
         message={t('dashboard.confirm.delete', { title: deleteTrip?.title || '' })}
       />
 
+      <CopyTripDialog
+        isOpen={!!copyTrip}
+        tripTitle={copyTrip?.title || ''}
+        onClose={() => setCopyTrip(null)}
+        onConfirm={confirmCopy}
+      />
+
       <style>{`
         @keyframes pulse {
           0%, 100% { opacity: 1 }