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>

SportsTime/Planning/Engine/ScenarioAPlanner.swift

@@ -81,14 +81,21 @@ final class ScenarioAPlanner: ScenarioPlanner {
         // Get all games that fall within the user's travel dates.
         // Sort by start time so we visit them in chronological order.
         let selectedRegions = request.preferences.selectedRegions
+        var gamesWithMissingStadium = 0
         let gamesInRange = request.allGames
             .filter { game in
                 // Must be in date range
                 guard dateRange.contains(game.startTime) else { return false }
 
+                // Track games with missing stadium data
+                guard request.stadiums[game.stadiumId] != nil else {
+                    gamesWithMissingStadium += 1
+                    return false
+                }
+
                 // Must be in selected region (if regions specified)
                 if !selectedRegions.isEmpty {
-                    guard let stadium = request.stadiums[game.stadiumId] else { return false }
+                    let stadium = request.stadiums[game.stadiumId]!
                     let gameRegion = Region.classify(longitude: stadium.coordinate.longitude)
                     return selectedRegions.contains(gameRegion)
                 }
@@ -98,10 +105,18 @@ final class ScenarioAPlanner: ScenarioPlanner {
 
         // No games? Nothing to plan.
         if gamesInRange.isEmpty {
+            var violations: [ConstraintViolation] = []
+            if gamesWithMissingStadium > 0 {
+                violations.append(ConstraintViolation(
+                    type: .missingData,
+                    description: "\(gamesWithMissingStadium) game(s) excluded due to missing stadium data",
+                    severity: .warning
+                ))
+            }
             return .failure(
                 PlanningFailure(
                     reason: .noGamesInRange,
-                    violations: []
+                    violations: violations
                 )
             )
         }
@@ -165,6 +180,7 @@ final class ScenarioAPlanner: ScenarioPlanner {
             from: filteredGames,
             stadiums: request.stadiums,
             allowRepeatCities: request.preferences.allowRepeatCities,
+            routePreference: request.preferences.routePreference,
             stopBuilder: buildStops
         )
         validRoutes.append(contentsOf: globalRoutes)
@@ -173,7 +189,8 @@ final class ScenarioAPlanner: ScenarioPlanner {
         let regionalRoutes = findRoutesPerRegion(
             games: filteredGames,
             stadiums: request.stadiums,
-            allowRepeatCities: request.preferences.allowRepeatCities
+            allowRepeatCities: request.preferences.allowRepeatCities,
+            routePreference: request.preferences.routePreference
         )
         validRoutes.append(contentsOf: regionalRoutes)
 
@@ -478,7 +495,8 @@ final class ScenarioAPlanner: ScenarioPlanner {
     private func findRoutesPerRegion(
         games: [Game],
         stadiums: [String: Stadium],
-        allowRepeatCities: Bool
+        allowRepeatCities: Bool,
+        routePreference: RoutePreference = .balanced
     ) -> [[Game]] {
         // Partition games by region
         var gamesByRegion: [Region: [Game]] = [:]
@@ -510,6 +528,7 @@ final class ScenarioAPlanner: ScenarioPlanner {
                 from: regionGames,
                 stadiums: stadiums,
                 allowRepeatCities: allowRepeatCities,
+                routePreference: routePreference,
                 stopBuilder: buildStops
             )