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/GameDAGRouter.swift

@@ -23,6 +23,26 @@
 import Foundation
 import CoreLocation
 
+/// DAG-based route finder for multi-game trips.
+///
+/// Finds time-respecting paths through a graph of games with driving feasibility
+/// and multi-dimensional diversity selection.
+///
+/// - Expected Behavior:
+///   - Empty games → empty result
+///   - Single game → [[game]] if no anchors or game is anchor
+///   - Two games → [[sorted]] if transition feasible and anchors satisfied
+///   - All routes are chronologically ordered
+///   - All routes respect driving constraints
+///   - Anchor games MUST appear in all returned routes
+///   - allowRepeatCities=false → no city appears twice in same route
+///   - Returns diverse set spanning games, cities, miles, and duration
+///
+/// - Invariants:
+///   - All returned routes have games in chronological order
+///   - All games in a route have feasible transitions between consecutive games
+///   - Maximum 75 routes returned (maxOptions)
+///   - Routes with anchor games include ALL anchor games
 enum GameDAGRouter {
 
     // MARK: - Configuration
@@ -104,6 +124,16 @@ enum GameDAGRouter {
     ///
     /// - Returns: Array of diverse route options
     ///
+    /// - Expected Behavior:
+    ///   - Empty games → empty result
+    ///   - Single game with no anchors → [[game]]
+    ///   - Single game that is the anchor → [[game]]
+    ///   - Single game not matching anchor → []
+    ///   - Two feasible games → [[game1, game2]] (chronological order)
+    ///   - Two infeasible games (no anchors) → [[game1], [game2]] (separate routes)
+    ///   - Two infeasible games (with anchors) → [] (can't satisfy)
+    ///   - anchorGameIds must be subset of any returned route
+    ///   - allowRepeatCities=false filters routes with duplicate cities
     static func findRoutes(
         games: [Game],
         stadiums: [String: Stadium],