feat(wizard): add TripWizardViewModel with reveal state logic

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

SportsTimeTests/Trip/TripWizardViewModelTests.swift

@@ -0,0 +1,48 @@
+//
+//  TripWizardViewModelTests.swift
+//  SportsTimeTests
+//
+
+import XCTest
+@testable import SportsTime
+
+final class TripWizardViewModelTests: XCTestCase {
+
+    func test_initialState_onlyPlanningModeStepVisible() {
+        let viewModel = TripWizardViewModel()
+
+        XCTAssertTrue(viewModel.isPlanningModeStepVisible)
+        XCTAssertFalse(viewModel.isSportsStepVisible)
+        XCTAssertFalse(viewModel.isDatesStepVisible)
+        XCTAssertFalse(viewModel.isRegionsStepVisible)
+    }
+
+    func test_selectingPlanningMode_revealsSportsStep() {
+        let viewModel = TripWizardViewModel()
+
+        viewModel.planningMode = .dateRange
+
+        XCTAssertTrue(viewModel.isSportsStepVisible)
+    }
+
+    func test_selectingSport_revealsDatesStep() {
+        let viewModel = TripWizardViewModel()
+        viewModel.planningMode = .dateRange
+
+        viewModel.selectedSports = [.mlb]
+
+        XCTAssertTrue(viewModel.isDatesStepVisible)
+    }
+
+    func test_changingPlanningMode_resetsDownstreamSelections() {
+        let viewModel = TripWizardViewModel()
+        viewModel.planningMode = .dateRange
+        viewModel.selectedSports = [.mlb, .nba]
+        viewModel.hasSetDates = true
+
+        viewModel.planningMode = .gameFirst
+
+        XCTAssertTrue(viewModel.selectedSports.isEmpty)
+        XCTAssertFalse(viewModel.hasSetDates)
+    }
+}