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/components/Trips/TripMembersModal.jsx

@@ -144,7 +144,7 @@ export default function TripMembersModal({ isOpen, onClose, tripId, tripTitle })
               disabled={adding || !selectedUserId}
               style={{
                 display: 'flex', alignItems: 'center', gap: 5, padding: '8px 14px',
-                background: 'var(--accent)', color: 'white', border: 'none', borderRadius: 10,
+                background: 'var(--accent)', color: 'var(--accent-text)', border: 'none', borderRadius: 10,
                 fontSize: 13, fontWeight: 600, cursor: adding || !selectedUserId ? 'default' : 'pointer',
                 fontFamily: 'inherit', opacity: adding || !selectedUserId ? 0.4 : 1, flexShrink: 0,
               }}