feat: decouple market from shared_lib, add app-owned models

Phase 1-3 of decoupling:
- path_setup.py adds project root to sys.path
- Market-owned models in market/models/ (market, market_place)
- All imports updated: shared.infrastructure, shared.db, shared.browser, etc.
- MarketPlace uses container_type/container_id instead of post_id FK

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

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