test(ensemble): cover navigateViewGroup clamp, CDN stale refresh, storage clear

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Risky behavior now covered

• navigateViewGroup index clamping — Prevents PageController.jumpToPage assertions when script-provided viewIndex exceeds the tab range (regression from #0ce6723a).
• CDN stale refresh race condition — Ensures cold-start manifest updates either sync the app bundle immediately or defer to resume, instead of firing refresh before resources are ready (regression from #19b50b2e).
• CDN manifest freshness gating — Locks in timestamp comparison logic that decides whether to re-fetch the CDN manifest.
• ensemble.storage.clear() dispatch ordering — Verifies binding notifications run only after async public storage removal completes, so listeners do not read stale values (regression from #8c2a52de).

Test files added/updated

File	Change
modules/ensemble/test/safe_view_group_payload_index_test.dart	Added resolveNavigateViewGroupTabIndex cases
modules/ensemble/test/cdn_provider_test.dart	Added stale refresh immediate vs deferred paths
modules/ensemble/test/cdn_manifest_freshness_test.dart	New — isCdnManifestIncomingNewer unit tests
modules/ensemble/test/ensemble_storage_clear_dispatch_test.dart	New — runEnsembleStorageClearDispatches ordering tests

Why these tests materially reduce regression risk

These areas are high blast-radius core flows (navigation, CDN updates, storage bindings) that were fixed recently with production-only changes. The extracted @visibleForTesting helpers let us assert the exact decision logic in isolation — no widgets, network, or Workmanager — so future refactors cannot silently reintroduce out-of-range tab jumps, CDN refresh races, or premature storage binding dispatches.

Validation

flutter test test/safe_view_group_payload_index_test.dart \
  test/cdn_manifest_freshness_test.dart \
  test/ensemble_storage_clear_dispatch_test.dart \
  test/cdn_provider_test.dart

All 20 tests passed.