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/nav.py

@@ -5,7 +5,7 @@ import re
 from typing import Dict, List, Tuple, Optional
 from urllib.parse import urlparse, urljoin
 
-from config import config
+from shared.config import config
 from . import db_backend as cb
 from .blacklist.category import is_category_blocked  # Reverse map: slug -> label