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/plugins/builtins/ai_proactive/models.py

@@ -64,7 +64,7 @@ class ProactiveSuggestion(Base, TenantMixin, OwnedMixin):
     )
 
 
-class ContextLog(Base, TenantMixin):
+class ContextLog(Base, TenantMixin, OwnedMixin):
     """Log of user context changes (page views, entity selections)."""
 
     __tablename__ = "ai_proactive_context_log"
@@ -86,7 +86,7 @@ class ContextLog(Base, TenantMixin):
     )
 
 
-class ProactiveSettings(Base, TenantMixin):
+class ProactiveSettings(Base, TenantMixin, OwnedMixin):
     """Per-user settings for proactive AI."""
 
     __tablename__ = "ai_proactive_settings"