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>

scrape/product/helpers/html.py

@@ -2,7 +2,7 @@
 from __future__ import annotations
 from typing import List, Optional
 from urllib.parse import urljoin, urlparse
-from config import config
+from shared.config import config
 
 def first_from_srcset(val: str) -> Optional[str]:
     if not val: