refactor(tests): TDD rewrite of all unit tests with spec documentation

Complete rewrite of unit test suite using TDD methodology:

Planning Engine Tests:
- GameDAGRouterTests: Beam search, anchor games, transitions
- ItineraryBuilderTests: Stop connection, validators, EV enrichment
- RouteFiltersTests: Region, time window, scoring filters
- ScenarioA/B/C/D PlannerTests: All planning scenarios
- TravelEstimatorTests: Distance, duration, travel days
- TripPlanningEngineTests: Orchestration, caching, preferences

Domain Model Tests:
- AchievementDefinitionsTests, AnySportTests, DivisionTests
- GameTests, ProgressTests, RegionTests, StadiumTests
- TeamTests, TravelSegmentTests, TripTests, TripPollTests
- TripPreferencesTests, TripStopTests, SportTests

Service Tests:
- FreeScoreAPITests, RouteDescriptionGeneratorTests
- SuggestedTripsGeneratorTests

Export Tests:
- ShareableContentTests (card types, themes, dimensions)

Bug fixes discovered through TDD:
- ShareCardDimensions: mapSnapshotSize exceeded available width (960x480)
- ScenarioBPlanner: Added anchor game validation filter

All tests include:
- Specification tests (expected behavior)
- Invariant tests (properties that must always hold)
- Edge case tests (boundary conditions)

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

SportsTime/Planning/Engine/TripPlanningEngine.swift

@@ -9,6 +9,19 @@ import Foundation
 
 /// Main entry point for trip planning.
 /// Delegates to scenario-specific planners via the ScenarioPlanner protocol.
+///
+/// - Expected Behavior:
+///   - Uses ScenarioPlannerFactory.planner(for:) to select the right planner
+///   - Delegates entirely to the selected scenario planner
+///   - Applies repeat city filter to successful results
+///   - If all options violate repeat city constraint → .failure with .repeatCityViolation
+///   - Passes through failures from scenario planners unchanged
+///
+/// - Invariants:
+///   - Never modifies the logic of scenario planners
+///   - Always returns a result (success or failure), never throws
+///   - Repeat city filter only applied when allowRepeatCities is false
+///
 final class TripPlanningEngine {
 
     /// Plans itineraries based on the request inputs.