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/ScenarioEPlanner.swift

@@ -90,9 +90,16 @@ final class ScenarioEPlanner: ScenarioPlanner {
         // the user wants to visit each team's home stadium.
         var homeGamesByTeam: [String: [Game]] = [:]
         var allHomeGames: [Game] = []
+        let selectedRegions = request.preferences.selectedRegions
 
         for game in request.allGames {
             if selectedTeamIds.contains(game.homeTeamId) {
+                // Apply region filter if regions are specified
+                if !selectedRegions.isEmpty {
+                    guard let stadium = request.stadiums[game.stadiumId] else { continue }
+                    let gameRegion = Region.classify(longitude: stadium.coordinate.longitude)
+                    guard selectedRegions.contains(gameRegion) else { continue }
+                }
                 homeGamesByTeam[game.homeTeamId, default: []].append(game)
                 allHomeGames.append(game)
             }
@@ -212,6 +219,7 @@ final class ScenarioEPlanner: ScenarioPlanner {
                 stadiums: request.stadiums,
                 anchorGameIds: earliestAnchorIds,
                 allowRepeatCities: request.preferences.allowRepeatCities,
+                routePreference: request.preferences.routePreference,
                 stopBuilder: buildStops
             )
             var validRoutes = candidateRoutes.filter { route in
@@ -230,6 +238,7 @@ final class ScenarioEPlanner: ScenarioPlanner {
                         stadiums: request.stadiums,
                         anchorGameIds: latestAnchorIds,
                         allowRepeatCities: request.preferences.allowRepeatCities,
+                        routePreference: request.preferences.routePreference,
                         stopBuilder: buildStops
                     )
                     candidateRoutes.append(contentsOf: latestAnchorRoutes)
@@ -239,6 +248,7 @@ final class ScenarioEPlanner: ScenarioPlanner {
                     from: uniqueGames,
                     stadiums: request.stadiums,
                     allowRepeatCities: request.preferences.allowRepeatCities,
+                    routePreference: request.preferences.routePreference,
                     stopBuilder: buildStops
                 )
                 candidateRoutes.append(contentsOf: noAnchorRoutes)