fix(di): robust all-or-nothing init so the social layer never greys out

The idempotency guard used SocialService as its sentinel, but that was
registered mid-cascade, so a run that crashed part-way could leave a
half-built container the next run would reuse (or hit 'already
registered' on) — intermittently falling back to the inventory-only look
with market/chat/profile greyed out.

- Guard on a dedicated _DepsReady marker registered LAST, so the sentinel
  means the WHOLE container is wired, never a partial one.
- Reset a half-wired container (crashed prior run) before rebuilding,
  instead of reusing it. Safe: main aborts before runApp on a partial run.
- Make the social key derivation non-fatal: on failure the app opens on
  inventory (social hidden) rather than blanking. main tolerates an
  absent SocialService.

apps/app_seeds/lib/main.dart

@@ -32,7 +32,9 @@ Future<void> main() async {
         repository: getIt<VarietyRepository>(),
         species: getIt<SpeciesRepository>(),
         onboarding: onboarding,
-        social: getIt<SocialService>(),
+        social: getIt.isRegistered<SocialService>()
+            ? getIt<SocialService>()
+            : null,
         socialSettings: getIt<SocialSettings>(),
         location: const GeolocatorCoarseLocation(),
         outbox: getIt<OfferOutbox>(),