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/slugs.py

@@ -1,6 +1,6 @@
 import re
 from urllib.parse import urljoin, urlparse
-from config import config
+from shared.config import config
 
 def product_slug_from_href(href: str) -> str:
     p = urlparse(href)