chore: fix all ruff lint warnings (unused imports, unsorted imports, unused vars)

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

web/tests/conftest.py

@@ -1,8 +1,6 @@
 """
 Shared test fixtures for the BeanFlows test suite.
 """
-import hashlib
-import hmac
 from datetime import datetime
 from pathlib import Path
 from unittest.mock import AsyncMock, patch
@@ -10,11 +8,9 @@ from unittest.mock import AsyncMock, patch
 import aiosqlite
 import pytest
 
-
 from beanflows import core
 from beanflows.app import create_app
 
-
 SCHEMA_PATH = Path(__file__).parent.parent / "src" / "beanflows" / "migrations" / "schema.sql"