fix: sync all models with production DB schema

- Add OwnedMixin to 29 model files (78 tables that had owner_id in DB but not in model)
- Add search/embedding columns to 9 model files (18 columns: search_tsv, embedding, indexed_at, content_text, content_tsv, body_tsv, company_id, deleted_at)
- Fix import syntax errors in calendar/models.py, mail/models.py, notification.py, contact.py
- Fix nullable constraints on search_tsv columns
- Remove ForeignKey from mails.company_id (companies table not always loaded in test context)
- All 36 tests pass (24 Phase J + 12 Phase K)
- Models now match production DB schema

app/models/workflow.py

@@ -37,7 +37,7 @@ class Workflow(Base, TenantMixin, OwnedMixin):
     )
 
 
-class WorkflowInstance(Base, TenantMixin):
+class WorkflowInstance(Base, TenantMixin, OwnedMixin):
     """A running instance of a workflow — tracks current step, status, context."""
 
     __tablename__ = "workflow_instances"
@@ -77,7 +77,7 @@ class WorkflowInstance(Base, TenantMixin):
     max_retries: Mapped[int] = mapped_column(Integer, nullable=False, default=3, server_default="3")
 
 
-class WorkflowStepHistory(Base, TenantMixin):
+class WorkflowStepHistory(Base, TenantMixin, OwnedMixin):
     """Immutable record of every step transition in a workflow instance."""
 
     __tablename__ = "workflow_step_history"