test: Add statistics test with manual data insertion

- TestStatisticsEndpoints: tests /api/v1/statistics/summary endpoint
- TestPartialMigrationThenSyncThenComplete: tests migration + sync workflow
- insertTestData: helper to insert 5 soundtracks with 8 songs
- getTestToken: helper to get auth token for tests
- Updated other test files to use FindAllSoundtracks instead of FindAllGames

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

internal/server/zz_music_handler_test.go

@@ -16,7 +16,7 @@ import (
 // ensureSyncRan ensures that sync has been run before testing music endpoints
 func ensureSyncRan(t *testing.T, e *echo.Echo) {
 	repo := repository.New(backend.BackendPool())
-	games, err := repo.FindAllGames(backend.BackendCtx())
+	games, err := repo.FindAllSoundtracks(backend.BackendCtx())
 	assert.NoError(t, err)
 
 	if len(games) == 0 {