fix: resolve architecture validation errors

- Create platform_service.py to move DB queries from platforms.py API
- Create platform.py exceptions for PlatformNotFoundException
- Update platforms.py API to use platform_service
- Update vendor/content_pages.py to use vendor_service
- Add get_vendor_by_id_optional method to VendorService
- Fix platforms.js: add centralized logger and init guard
- Fix content-page-edit.html: use modal macro instead of inline modal

All 21 architecture validation errors resolved.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

app/api/v1/vendor/content_pages.py

@@ -19,8 +19,11 @@ from sqlalchemy.orm import Session
 
 from app.api.deps import get_current_vendor_api, get_db
 from app.services.content_page_service import content_page_service
+from app.services.vendor_service import VendorService
 from models.database.user import User
 
+vendor_service = VendorService()
+
 router = APIRouter(prefix="/content-pages")
 logger = logging.getLogger(__name__)
 
@@ -272,9 +275,7 @@ def get_cms_usage(
 
     Returns page counts and limits based on subscription tier.
     """
-    from models.database.vendor import Vendor
-
-    vendor = db.query(Vendor).filter(Vendor.id == current_user.token_vendor_id).first()
+    vendor = vendor_service.get_vendor_by_id_optional(db, current_user.token_vendor_id)
     if not vendor:
         return CMSUsageResponse(
             total_pages=0,
@@ -336,10 +337,8 @@ def get_platform_default(
 
     Useful for vendors to view the original before/after overriding.
     """
-    from models.database.vendor import Vendor
-
     # Get vendor's platform
-    vendor = db.query(Vendor).filter(Vendor.id == current_user.token_vendor_id).first()
+    vendor = vendor_service.get_vendor_by_id_optional(db, current_user.token_vendor_id)
     platform_id = 1  # Default to OMS
 
     if vendor and vendor.platforms: