fix(tests): Remove AIChatSession/AIChatMessage imports, skip ai_copilot tests, fix OwnedMixin import

- test_ai_proactive.py: Remove AIChatSession/AIChatMessage/AIChatFolder/AIChatAttachment imports
- test_ai_copilot.py: Skip all tests (ai_copilot routes removed in Phase 2)
- test_permission_system_live.py: Guard AIConversation/AIMessage import with try/except
- conftest.py: Guard AIConversation/AIMessage import with try/except
- unified_search/models.py: Add missing OwnedMixin import
- test_ai_proactive.py: Skip test_rate_limiting (get_cache removed)

tests/test_permission_system_live.py

@@ -74,7 +74,10 @@ from app.plugins.builtins.tags.models import Tag, TagAssignment  # noqa: F401
 from app.plugins.builtins.entity_links.models import EntityLink  # noqa: F401
 from app.plugins.builtins.report_generator import ReportGeneratorPlugin  # noqa: F401
 from app.plugins.builtins.report_generator.models import ReportInstance, ReportTemplate  # noqa: F401
-from app.models.ai_conversation import AIConversation, AIMessage  # noqa: F401
+try:
+    from app.models.ai_conversation import AIConversation, AIMessage  # noqa: F401
+except ImportError:
+    pass
 from app.models.contact_merge import ContactMergeHistory  # noqa: F401
 from app.models.plugin import Plugin, PluginMigration  # noqa: F401
 from app.models.user_preference import UserPreference  # noqa: F401