Budget: per-person expense tracking with member chips

- New budget_item_members junction table (migration 27)
- Assign trip members to budget items via avatar chips in Persons column
- Per-person split auto-calculated from assigned member count
- Per-person summary integrated into total budget card
- Member chips rendered via portal dropdown (no overflow clipping)
- Mobile: larger touch-friendly chips (30px) under item name
- Desktop: compact chips (20px) in Persons column
- Custom NOMAD-style tooltips on chips
- WebSocket live sync for all member operations
- Fix invite button text color in dark mode
- Widen budget layout to 1800px max-width
- Shorten "Per Person/Day" column header

client/src/pages/TripPlannerPage.jsx

@@ -675,8 +675,8 @@ export default function TripPlannerPage() {
         )}
 
         {activeTab === 'finanzplan' && (
-          <div style={{ height: '100%', overflowY: 'auto', overscrollBehavior: 'contain', maxWidth: 1400, margin: '0 auto', width: '100%', padding: '8px 0' }}>
-            <BudgetPanel tripId={tripId} />
+          <div style={{ height: '100%', overflowY: 'auto', overscrollBehavior: 'contain', maxWidth: 1800, margin: '0 auto', width: '100%', padding: '8px 0' }}>
+            <BudgetPanel tripId={tripId} tripMembers={tripMembers} />
           </div>
         )}