fix: test isolation + auth import compatibility + add optuna to requirements (HRT-136)

Test isolation fixes:
- auth_db.get_db(): read TURF_SAAS_DB dynamically (not frozen at import)
- api_v1/utils.get_db(): read TURF_SAAS_DB dynamically (not frozen at import)
- api_tokens_db.get_db(): read TURF_SAAS_DB dynamically (not frozen at import)
- tests/test_history.py: enforce _tmp_db.name + call init_auth_tables() in fixtures
- tests/test_user_tokens.py: enforce _tmp_db.name + call migrate_api_tokens_tables() in app fixture

Auth compatibility fixes:
- api_v1/routes/history.py: use auth.jwt_required_middleware (flask_jwt_extended)
  with saas_auth fallback for portal_server context
- api_v1/routes/ml_feedback.py: same auth import strategy
- api_v1/routes/user.py: same auth import strategy

Dependencies:
- requirements.txt: add optuna>=4.0.0 (used in ML ensemble tests and training)

Co-Authored-By: Paperclip <noreply@paperclip.ing>

api_tokens_db.py

@@ -13,7 +13,9 @@ logger = logging.getLogger("turf_saas.api_tokens_db")
 
 
 def get_db() -> sqlite3.Connection:
-    conn = sqlite3.connect(DB_PATH)
+    """Return a SQLite connection (reads TURF_SAAS_DB dynamically for test isolation)."""
+    db_path = os.environ.get("TURF_SAAS_DB", DB_PATH)
+    conn = sqlite3.connect(db_path)
     conn.row_factory = sqlite3.Row
     return conn