Remove auth blueprint, federation is now an OAuth client

Auth server responsibilities moved to account app.
Federation uses the shared OAuth client blueprint via factory.

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

market/models/__init__.py

@@ -0,0 +1,8 @@
+from .market import (
+    Product, ProductLike, ProductImage, ProductSection,
+    NavTop, NavSub, Listing, ListingItem,
+    LinkError, LinkExternal, SubcategoryRedirect, ProductLog,
+    ProductLabel, ProductSticker, ProductAttribute, ProductNutrition, ProductAllergen,
+    CartItem,
+)
+from .market_place import MarketPlace