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/tenancy/services/platform_service.py

@@ -17,7 +17,6 @@ from dataclasses import dataclass
 from sqlalchemy import func
 from sqlalchemy.orm import Session
 
-from app.modules.cms.models import ContentPage
 from app.modules.tenancy.exceptions import (
     PlatformNotFoundException,
 )
@@ -102,6 +101,11 @@ class PlatformService:
 
         return platform
 
+    @staticmethod
+    def get_default_platform(db: Session) -> Platform | None:
+        """Get the first/default platform."""
+        return db.query(Platform).first()
+
     @staticmethod
     def list_platforms(
         db: Session, include_inactive: bool = False
@@ -167,6 +171,13 @@ class PlatformService:
             or 0
         )
 
+    @staticmethod
+    def _get_content_page_model():
+        """Deferred import for CMS ContentPage model."""
+        from app.modules.cms.models import ContentPage
+
+        return ContentPage
+
     @staticmethod
     def get_platform_pages_count(db: Session, platform_id: int) -> int:
         """
@@ -179,6 +190,7 @@ class PlatformService:
         Returns:
             Platform pages count
         """
+        ContentPage = PlatformService._get_content_page_model()
         return (
             db.query(func.count(ContentPage.id))
             .filter(
@@ -202,6 +214,7 @@ class PlatformService:
         Returns:
             Store defaults count
         """
+        ContentPage = PlatformService._get_content_page_model()
         return (
             db.query(func.count(ContentPage.id))
             .filter(
@@ -225,6 +238,7 @@ class PlatformService:
         Returns:
             Store overrides count
         """
+        ContentPage = PlatformService._get_content_page_model()
         return (
             db.query(func.count(ContentPage.id))
             .filter(
@@ -247,6 +261,7 @@ class PlatformService:
         Returns:
             Published pages count
         """
+        ContentPage = PlatformService._get_content_page_model()
         return (
             db.query(func.count(ContentPage.id))
             .filter(
@@ -269,6 +284,7 @@ class PlatformService:
         Returns:
             Draft pages count
         """
+        ContentPage = PlatformService._get_content_page_model()
         return (
             db.query(func.count(ContentPage.id))
             .filter(
@@ -303,6 +319,187 @@ class PlatformService:
             draft_pages_count=cls.get_draft_pages_count(db, platform.id),
         )
 
+    # ========================================================================
+    # StorePlatform cross-module public API methods
+    # ========================================================================
+
+    @staticmethod
+    def get_primary_platform_id_for_store(db: Session, store_id: int) -> int | None:
+        """
+        Get the primary platform ID for a store.
+
+        Args:
+            db: Database session
+            store_id: Store ID
+
+        Returns:
+            Platform ID or None if no platform assigned
+        """
+        result = (
+            db.query(StorePlatform.platform_id)
+            .filter(
+                StorePlatform.store_id == store_id,
+                StorePlatform.is_active == True,  # noqa: E712
+            )
+            .order_by(StorePlatform.is_primary.desc())
+            .first()
+        )
+        return result[0] if result else None
+
+    @staticmethod
+    def get_active_platform_ids_for_store(db: Session, store_id: int) -> list[int]:
+        """
+        Get all active platform IDs for a store.
+
+        Args:
+            db: Database session
+            store_id: Store ID
+
+        Returns:
+            List of platform IDs
+        """
+        results = (
+            db.query(StorePlatform.platform_id)
+            .filter(
+                StorePlatform.store_id == store_id,
+                StorePlatform.is_active == True,  # noqa: E712
+            )
+            .order_by(StorePlatform.is_primary.desc())
+            .all()
+        )
+        return [r[0] for r in results]
+
+    @staticmethod
+    def get_store_platform_entry(
+        db: Session, store_id: int, platform_id: int
+    ) -> StorePlatform | None:
+        """
+        Get a specific StorePlatform entry.
+
+        Args:
+            db: Database session
+            store_id: Store ID
+            platform_id: Platform ID
+
+        Returns:
+            StorePlatform object or None
+        """
+        return (
+            db.query(StorePlatform)
+            .filter(
+                StorePlatform.store_id == store_id,
+                StorePlatform.platform_id == platform_id,
+            )
+            .first()
+        )
+
+    @staticmethod
+    def get_primary_store_platform_entry(
+        db: Session, store_id: int
+    ) -> StorePlatform | None:
+        """
+        Get the primary StorePlatform entry for a store.
+
+        Args:
+            db: Database session
+            store_id: Store ID
+
+        Returns:
+            StorePlatform object or None
+        """
+        return (
+            db.query(StorePlatform)
+            .filter(
+                StorePlatform.store_id == store_id,
+                StorePlatform.is_primary.is_(True),
+            )
+            .first()
+        )
+
+    @staticmethod
+    def get_store_ids_for_platform(
+        db: Session, platform_id: int, active_only: bool = True
+    ) -> list[int]:
+        """
+        Get store IDs subscribed to a platform.
+
+        Args:
+            db: Database session
+            platform_id: Platform ID
+            active_only: Only return active store-platform links
+
+        Returns:
+            List of store IDs
+        """
+        query = db.query(StorePlatform.store_id).filter(
+            StorePlatform.platform_id == platform_id,
+        )
+        if active_only:
+            query = query.filter(StorePlatform.is_active == True)  # noqa: E712
+        return [r[0] for r in query.all()]
+
+    @staticmethod
+    def ensure_store_platform(
+        db: Session,
+        store_id: int,
+        platform_id: int,
+        is_active: bool,
+        tier_id: int | None = None,
+    ) -> StorePlatform | None:
+        """
+        Upsert a StorePlatform entry.
+
+        If the entry exists, update is_active (and tier_id if provided).
+        If missing and is_active=True, create it (set is_primary if store has none).
+        If missing and is_active=False, no-op.
+
+        Args:
+            db: Database session
+            store_id: Store ID
+            platform_id: Platform ID
+            is_active: Whether the store-platform link is active
+            tier_id: Optional subscription tier ID
+
+        Returns:
+            The StorePlatform entry, or None if no-op
+        """
+        existing = (
+            db.query(StorePlatform)
+            .filter(
+                StorePlatform.store_id == store_id,
+                StorePlatform.platform_id == platform_id,
+            )
+            .first()
+        )
+
+        if existing:
+            existing.is_active = is_active
+            if tier_id is not None:
+                existing.tier_id = tier_id
+            return existing
+
+        if is_active:
+            has_primary = (
+                db.query(StorePlatform)
+                .filter(
+                    StorePlatform.store_id == store_id,
+                    StorePlatform.is_primary.is_(True),
+                )
+                .first()
+            ) is not None
+
+            sp = StorePlatform(
+                store_id=store_id,
+                platform_id=platform_id,
+                is_active=True,
+                is_primary=not has_primary,
+                tier_id=tier_id,
+            )
+            db.add(sp)
+            return sp
+
+        return None
+
     @staticmethod
     def update_platform(
         db: Session, platform: Platform, update_data: dict