refactor(arch): eliminate all cross-module model imports in service layer

Enforce MOD-025/MOD-026 rules: zero top-level cross-module model imports
remain in any service file. All 66 files migrated using deferred import
patterns (method-body, _get_model() helpers, instance-cached self._Model)
and new cross-module service methods in tenancy. Documentation updated
with Pattern 6 (deferred imports), migration plan marked complete, and
violations status reflects 84→0 service-layer violations.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

app/modules/messaging/services/admin_notification_service.py

@@ -8,6 +8,8 @@ Provides functionality for:
 - Notification statistics and queries
 """
 
+from __future__ import annotations
+
 import logging
 from datetime import datetime, timedelta
 from typing import Any
@@ -16,7 +18,6 @@ from sqlalchemy import and_, case
 from sqlalchemy.orm import Session
 
 from app.modules.messaging.models.admin_notification import AdminNotification
-from app.modules.tenancy.models import PlatformAlert
 from app.modules.tenancy.schemas.admin import (
     AdminNotificationCreate,
     PlatformAlertCreate,
@@ -25,6 +26,13 @@ from app.modules.tenancy.schemas.admin import (
 logger = logging.getLogger(__name__)
 
 
+def _get_platform_alert_model():
+    """Deferred import for PlatformAlert model (lives in tenancy, consumed by messaging)."""
+    from app.modules.tenancy.models import PlatformAlert
+
+    return PlatformAlert
+
+
 # ============================================================================
 # NOTIFICATION TYPES
 # ============================================================================
@@ -475,6 +483,7 @@ class PlatformAlertService:
         auto_generated: bool = True,
     ) -> PlatformAlert:
         """Create a new platform alert."""
+        PlatformAlert = _get_platform_alert_model()
         now = datetime.utcnow()
 
         alert = PlatformAlert(
@@ -527,6 +536,7 @@ class PlatformAlertService:
         Returns:
             Tuple of (alerts, total_count, active_count, critical_count)
         """
+        PlatformAlert = _get_platform_alert_model()
         query = db.query(PlatformAlert)
 
         # Apply filters
@@ -587,6 +597,7 @@ class PlatformAlertService:
         resolution_notes: str | None = None,
     ) -> PlatformAlert | None:
         """Resolve a platform alert."""
+        PlatformAlert = _get_platform_alert_model()
         alert = db.query(PlatformAlert).filter(PlatformAlert.id == alert_id).first()
 
         if alert and not alert.is_resolved:
@@ -602,6 +613,7 @@ class PlatformAlertService:
 
     def get_statistics(self, db: Session) -> dict[str, int]:
         """Get alert statistics."""
+        PlatformAlert = _get_platform_alert_model()
         today_start = datetime.utcnow().replace(hour=0, minute=0, second=0, microsecond=0)
 
         total = db.query(PlatformAlert).count()
@@ -644,6 +656,7 @@ class PlatformAlertService:
         alert_id: int,
     ) -> PlatformAlert | None:
         """Increment occurrence count for repeated alert."""
+        PlatformAlert = _get_platform_alert_model()
         alert = db.query(PlatformAlert).filter(PlatformAlert.id == alert_id).first()
 
         if alert:
@@ -660,6 +673,7 @@ class PlatformAlertService:
         title: str,
     ) -> PlatformAlert | None:
         """Find an active alert with same type and title."""
+        PlatformAlert = _get_platform_alert_model()
         return (
             db.query(PlatformAlert)
             .filter(