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/build_snapshot/build_snapshot.py

@@ -7,9 +7,9 @@ from typing import Dict, Set
 from ..http_client import configure_cookies
 from ..get_auth import login
 
-from config import config
+from shared.config import config
 
-from utils import log
+from shared.utils import log
 
 # DB: persistence helpers