Phase 2: Visibility Filter & Owner ID

- Add OwnedMixin to 15 models (contact_folder, user_preference, workspace,
  mcp_server_config, agent_definition, automation_definition, report_template,
  report_instance, entity_link, comm_conversation, proactive_suggestion,
  ai_agent, ai_chat_session, tag, share_link)
- Migration 0102: Add owner_id column to 15 tables with backfill from user_id
- Fix EntityPermission Registry: remove notification, add entity_attachment,
  entity_history, subtask, calendar, folder; fix wrong class names
  (DmsFile→File, CalendarEvent→CalendarEntry, Mailbox→MailAccount)
- Add apply_visibility_filter to list endpoints in tags, tasks, mcp_client,
  automation, report_generator, ai_assistant routes
- Add owner_id to create handlers for all new OwnedMixin models
- Patch tasks/services.py and automation/services.py list methods with
  user_id and is_system_admin parameters

app/plugins/builtins/ai_assistant/models.py

@@ -19,6 +19,7 @@ from sqlalchemy.dialects.postgresql import JSONB, UUID as PGUUID
 from sqlalchemy.orm import Mapped, mapped_column
 
 from app.core.db import Base, TenantMixin
+from app.models.owned_mixin import OwnedMixin
 
 
 # --- Providers ---
@@ -101,7 +102,7 @@ class AIPreset(Base, TenantMixin):
 
 # --- Agents ---
 
-class AIAgent(Base, TenantMixin):
+class AIAgent(Base, TenantMixin, OwnedMixin):
     """AI agent with system prompt and assigned tools."""
 
     __tablename__ = "ai_agents"
@@ -128,7 +129,7 @@ class AIAgent(Base, TenantMixin):
 
 # --- Chat Sessions ---
 
-class AIChatSession(Base, TenantMixin):
+class AIChatSession(Base, TenantMixin, OwnedMixin):
     """Chat session for a user with a specific agent."""
 
     __tablename__ = "ai_chat_sessions"