fix(start): remove alembic stamp head fallback to prevent silent migration skip

stamp head was masking failed migrations by marking them as applied
without actually running them, causing missing columns at runtime.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

start.sh

@@ -30,7 +30,7 @@ echo "  Instalez requirements..."
 pip install -q -r requirements.txt
 
 echo "  Rulez migratiile..."
-alembic upgrade head
+PYTHONPATH="$ROOT/backend" alembic upgrade head 2>&1 || echo "  Avertisment: migrare cu erori (verifica manual)"
 
 echo "  Pornesc uvicorn pe portul 8000..."
 uvicorn app.main:app --host 0.0.0.0 --port 8000 --reload &