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>

SportsTimeTests/Services/DataProviderTests.swift

@@ -0,0 +1,48 @@
+//
+//  DataProviderTests.swift
+//  SportsTimeTests
+//
+//  TDD specification tests for DataProvider types.
+//
+
+import Testing
+import Foundation
+@testable import SportsTime
+
+// MARK: - DataProviderError Tests
+
+@Suite("DataProviderError")
+struct DataProviderErrorTests {
+
+    // MARK: - Specification Tests: errorDescription
+
+    /// - Expected Behavior: contextNotConfigured has meaningful error message
+    @Test("errorDescription: contextNotConfigured mentions configuration")
+    func errorDescription_contextNotConfigured() {
+        let error = DataProviderError.contextNotConfigured
+        #expect(error.errorDescription != nil)
+        #expect(error.errorDescription!.lowercased().contains("configured") || error.errorDescription!.lowercased().contains("context"))
+    }
+
+    /// - Expected Behavior: error conforms to LocalizedError
+    @Test("DataProviderError: conforms to LocalizedError")
+    func dataProviderError_localizedError() {
+        let error: any LocalizedError = DataProviderError.contextNotConfigured
+        #expect(error.errorDescription != nil)
+    }
+
+    // MARK: - Invariant Tests
+
+    /// - Invariant: All errors have non-empty descriptions
+    @Test("Invariant: all errors have descriptions")
+    func invariant_allHaveDescriptions() {
+        let errors: [DataProviderError] = [
+            .contextNotConfigured
+        ]
+
+        for error in errors {
+            #expect(error.errorDescription != nil)
+            #expect(!error.errorDescription!.isEmpty)
+        }
+    }
+}