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/db_backend.py

@@ -4,7 +4,7 @@ from typing import Dict, List, Optional
 from sqlalchemy import select, and_
 from sqlalchemy.orm import selectinload
 
-from config import config  # if unused elsewhere, you can remove this import
+from shared.config import config  # if unused elsewhere, you can remove this import
 
 # ORM models
 from models.market import (