feat(trip): redesign add custom item UI with polished visuals

Replace confusing dual-mode AddItemSheet with streamlined QuickAddItemSheet:
- Single flow with optional location (vs Search/Custom toggle)
- Card-based layout with shadows, borders, and theme colors
- Enhanced CategoryPicker with emoji circles and press animations
- Separate PlaceSearchSheet for focused location search
- Improved header button with capsule style and accessibility labels

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

SportsTime/Features/Trip/Views/TripDetailView.swift

@@ -1934,7 +1934,7 @@ private struct SheetModifiers: ViewModifier {
                 PaywallView()
             }
             .sheet(item: $addItemAnchor) { anchor in
-                AddItemSheet(
+                QuickAddItemSheet(
                     tripId: tripId,
                     day: anchor.day,
                     existingItem: nil
@@ -1943,7 +1943,7 @@ private struct SheetModifiers: ViewModifier {
                 }
             }
             .sheet(item: $editingItem) { item in
-                AddItemSheet(
+                QuickAddItemSheet(
                     tripId: tripId,
                     day: item.day,
                     existingItem: item