Fix datetime deprecation warnings in Phase 8 modules

- Update all datetime.utcnow() to datetime.now(UTC) for Python 3.12+ compatibility
- Update all datetime.utcfromtimestamp() to datetime.fromtimestamp(..., UTC)
- Fix dataclass default_factory to use lambda: datetime.now(UTC)
- Update auth, audit, billing, and realtime modules
- Add UTC import from datetime module
- Update pytest configuration to include pytest-asyncio
- All 28 Phase 8 enterprise tests pass with no warnings

Co-Authored-By: Claude Haiku 4.5 <noreply@anthropic.com>

.claude/settings.local.json

@@ -34,7 +34,11 @@
       "Bash(git commit *)",
       "Bash(python test_phase5_entity_resolver.py)",
       "Bash(cd /d C:\\\\Users\\\\lasta\\\\MyProject\\\\AI\\\\.claude\\\\worktrees\\\\infallible-mayer-01d511)",
-      "Bash(python test_phase5_subgraph_retriever.py)"
+      "Bash(python test_phase5_subgraph_retriever.py)",
+      "Bash(python -m pytest tests/test_phase7_llm_integration.py -v --tb=short)",
+      "Bash(python -m pytest tests/test_phase7_llm_integration.py -v --tb=line)",
+      "Bash(python -m pytest tests/test_phase8_enterprise.py -v --tb=short)",
+      "Bash(python -m pytest tests/test_phase8_enterprise.py -v --tb=line)"
     ]
   }
 }