fix(project): stabilize python3 tests and app shutdown

Use python3/venv consistently for local test execution and
make package discovery deterministic for pytest.

Also migrate FastAPI shutdown handling to lifespan to remove
deprecation warnings while preserving cleanup behavior.

scripts/auto-test.sh

@@ -3,8 +3,18 @@ set -euo pipefail
 
 cd "$(dirname "$0")/.."
 
+if ! command -v python3 >/dev/null 2>&1; then
+  echo "python3 non trovato nel PATH." >&2
+  exit 1
+fi
+
+if [[ ! -x ".venv/bin/python3" ]]; then
+  echo "Creating virtual environment..."
+  python3 -m venv .venv
+fi
+
 echo "Installing dependencies..."
-python -m pip install -r requirements.txt >/dev/null
+.venv/bin/python3 -m pip install -r requirements.txt >/dev/null
 
 echo "Running pytest..."
-python -m pytest tests
+PYTHONPATH=. .venv/bin/python3 -m pytest tests