Add implementation code for all 4 improvement plan phases

Production changes:
- TravelEstimator: remove 300mi fallback, return nil on missing coords
- TripPlanningEngine: add warnings array, empty sports warning, inverted
  date range rejection, must-stop filter, segment validation gate
- GameDAGRouter: add routePreference parameter with preference-aware
  bucket ordering and sorting in selectDiverseRoutes()
- ScenarioA-E: pass routePreference through to GameDAGRouter
- ScenarioA: track games with missing stadium data
- ScenarioE: add region filtering for home games
- TravelSegment: add requiresOvernightStop and travelDays() helpers

Test changes:
- GameDAGRouterTests: +252 lines for route preference verification
- TripPlanningEngineTests: +153 lines for segment validation, date range,
  empty sports
- ScenarioEPlannerTests: +119 lines for region filter tests
- TravelEstimatorTests: remove obsolete fallback distance tests
- ItineraryBuilderTests: update nil-coords test expectation

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

SportsTimeTests/Planning/TripPlanningEngineTests.swift

@@ -146,6 +146,159 @@ struct TripPlanningEngineTests {
         }
     }
 
+    // MARK: - Travel Segment Validation
+
+    @Test("planTrip: multi-stop result always has travel segments")
+    func planTrip_multiStopResult_alwaysHasTravelSegments() {
+        let baseDate = TestFixtures.date(year: 2026, month: 6, day: 1, hour: 19, minute: 0)
+        let day2 = TestClock.calendar.date(byAdding: .day, value: 1, to: baseDate)!
+        let day3 = TestClock.calendar.date(byAdding: .day, value: 2, to: baseDate)!
+
+        let game1 = TestFixtures.game(city: "New York", dateTime: baseDate)
+        let game2 = TestFixtures.game(city: "Boston", dateTime: day2)
+        let game3 = TestFixtures.game(city: "Philadelphia", dateTime: day3)
+
+        let stadiums = TestFixtures.stadiumMap(for: [game1, game2, game3])
+
+        let prefs = TripPreferences(
+            planningMode: .dateRange,
+            sports: [.mlb],
+            startDate: baseDate,
+            endDate: day3
+        )
+
+        let request = PlanningRequest(
+            preferences: prefs,
+            availableGames: [game1, game2, game3],
+            teams: [:],
+            stadiums: stadiums
+        )
+
+        let engine = TripPlanningEngine()
+        let result = engine.planItineraries(request: request)
+
+        if case .success(let options) = result {
+            for option in options {
+                #expect(option.isValid, "Every returned option must be valid (segments = stops - 1)")
+                if option.stops.count > 1 {
+                    #expect(option.travelSegments.count == option.stops.count - 1)
+                }
+            }
+        }
+    }
+
+    @Test("planTrip: N stops always have exactly N-1 travel segments")
+    func planTrip_nStops_haveExactlyNMinus1Segments() {
+        let baseDate = TestFixtures.date(year: 2026, month: 6, day: 1, hour: 19, minute: 0)
+
+        // Create 5 games across cities to produce routes of varying lengths
+        let cities = ["New York", "Boston", "Philadelphia", "Chicago", "Detroit"]
+        var games: [Game] = []
+        for (i, city) in cities.enumerated() {
+            let date = TestClock.calendar.date(byAdding: .day, value: i, to: baseDate)!
+            games.append(TestFixtures.game(city: city, dateTime: date))
+        }
+
+        let stadiums = TestFixtures.stadiumMap(for: games)
+        let endDate = TestClock.calendar.date(byAdding: .day, value: cities.count, to: baseDate)!
+
+        let prefs = TripPreferences(
+            planningMode: .dateRange,
+            sports: [.mlb],
+            startDate: baseDate,
+            endDate: endDate
+        )
+
+        let request = PlanningRequest(
+            preferences: prefs,
+            availableGames: games,
+            teams: [:],
+            stadiums: stadiums
+        )
+
+        let engine = TripPlanningEngine()
+        let result = engine.planItineraries(request: request)
+
+        if case .success(let options) = result {
+            #expect(!options.isEmpty, "Should produce at least one option")
+            for option in options {
+                if option.stops.count > 1 {
+                    #expect(option.travelSegments.count == option.stops.count - 1,
+                           "Option with \(option.stops.count) stops must have exactly \(option.stops.count - 1) segments, got \(option.travelSegments.count)")
+                } else {
+                    #expect(option.travelSegments.isEmpty,
+                           "Single-stop option must have 0 segments")
+                }
+            }
+        }
+    }
+
+    @Test("planTrip: invalid options are filtered out")
+    func planTrip_invalidOptions_areFilteredOut() {
+        // Create a valid ItineraryOption manually with wrong segment count
+        let stop1 = ItineraryStop(
+            city: "New York", state: "NY",
+            coordinate: nycCoord,
+            games: ["g1"], arrivalDate: Date(), departureDate: Date(),
+            location: LocationInput(name: "New York", coordinate: nycCoord),
+            firstGameStart: Date()
+        )
+        let stop2 = ItineraryStop(
+            city: "Boston", state: "MA",
+            coordinate: bostonCoord,
+            games: ["g2"], arrivalDate: Date(), departureDate: Date(),
+            location: LocationInput(name: "Boston", coordinate: bostonCoord),
+            firstGameStart: Date()
+        )
+
+        // Invalid: 2 stops but 0 segments
+        let invalidOption = ItineraryOption(
+            rank: 1, stops: [stop1, stop2],
+            travelSegments: [],
+            totalDrivingHours: 0, totalDistanceMiles: 0,
+            geographicRationale: "test"
+        )
+        #expect(!invalidOption.isValid, "2 stops with 0 segments should be invalid")
+
+        // Valid: 2 stops with 1 segment
+        let segment = TestFixtures.travelSegment(from: "New York", to: "Boston")
+        let validOption = ItineraryOption(
+            rank: 1, stops: [stop1, stop2],
+            travelSegments: [segment],
+            totalDrivingHours: 3.5, totalDistanceMiles: 215,
+            geographicRationale: "test"
+        )
+        #expect(validOption.isValid, "2 stops with 1 segment should be valid")
+    }
+
+    @Test("planTrip: inverted date range returns failure")
+    func planTrip_invertedDateRange_returnsFailure() {
+        let endDate = TestFixtures.date(year: 2026, month: 6, day: 1)
+        let startDate = TestFixtures.date(year: 2026, month: 6, day: 10)
+
+        let prefs = TripPreferences(
+            planningMode: .dateRange,
+            sports: [.mlb],
+            startDate: startDate,
+            endDate: endDate
+        )
+
+        let request = PlanningRequest(
+            preferences: prefs,
+            availableGames: [],
+            teams: [:],
+            stadiums: [:]
+        )
+
+        let engine = TripPlanningEngine()
+        let result = engine.planItineraries(request: request)
+
+        #expect(!result.isSuccess)
+        if let failure = result.failure {
+            #expect(failure.reason == .missingDateRange)
+        }
+    }
+
     // MARK: - Helper Methods
 
     private func makeStadium(