refactor(wizard): show all steps at once with validation gating

- Replace progressive reveal with single fade-in of all steps
- Add canPlanTrip validation requiring all fields before planning
- Disable Plan Trip button until all selections are made
- Simplify ViewModel by removing step-by-step visibility logic
- Update tests for new validation-based approach

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

SportsTime/Features/Trip/Views/Wizard/Steps/ReviewStep.swift

@@ -18,6 +18,7 @@ struct ReviewStep: View {
     let allowRepeatCities: Bool
     let mustStopLocations: [LocationInput]
     let isPlanning: Bool
+    let canPlanTrip: Bool
     let onPlan: () -> Void
 
     var body: some View {
@@ -55,11 +56,11 @@ struct ReviewStep: View {
                 }
                 .frame(maxWidth: .infinity)
                 .padding(Theme.Spacing.md)
-                .background(Theme.warmOrange)
+                .background(canPlanTrip ? Theme.warmOrange : Theme.textMuted(colorScheme))
                 .foregroundStyle(.white)
                 .clipShape(RoundedRectangle(cornerRadius: Theme.CornerRadius.large))
             }
-            .disabled(isPlanning)
+            .disabled(!canPlanTrip || isPlanning)
         }
         .padding(Theme.Spacing.lg)
         .background(Theme.cardBackground(colorScheme))
@@ -113,6 +114,7 @@ private struct ReviewRow: View {
         allowRepeatCities: false,
         mustStopLocations: [],
         isPlanning: false,
+        canPlanTrip: true,
         onPlan: {}
     )
     .padding()