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>

bp/browse/services/services.py

@@ -6,11 +6,11 @@ from quart import (
     g,
     request,
 )
-from config import config
+from shared.config import config
 from .products import products, products_nocounts
 from .blacklist.product_details import is_blacklisted_heading
 
-from utils import host_url
+from shared.utils import host_url
 
 
 from sqlalchemy import select
@@ -163,7 +163,7 @@ def _massage_product(d):
 
 
 # Re-export from canonical shared location
-from shared.http_utils import vary as _vary, current_url_without_page as _current_url_without_page
+from shared.infrastructure.http_utils import vary as _vary, current_url_without_page as _current_url_without_page
 
 async def _is_liked(user_id: int | None, slug: str) -> bool:
     """