fix: resolve 57 ruff lint errors (unused imports, unused variables, import placement)

tests/test_auth.py

@@ -1,7 +1,4 @@
 # tests/test_auth.py — Tests for authentication and authorization
-import os
-import time
-from unittest.mock import patch
 
 import pytest
 
@@ -70,9 +67,7 @@ class TestJWTHandler:
         from backend.auth.jwt_handler import (
             create_access_token,
             decode_token,
-            ACCESS_TOKEN_EXPIRE_SECONDS,
         )
-        import time
 
         # Override TTL to a value in the past
         user = {"username": "testuser", "role": "user", "vaults": [], "display_name": "X"}
@@ -111,7 +106,6 @@ class TestJWTHandler:
     def test_wrong_type_token(self):
         """decode_token rejects refresh tokens (type != 'access')."""
         from backend.auth.jwt_handler import (
-            create_access_token,
             create_refresh_token,
             decode_token,
         )
@@ -229,7 +223,7 @@ class TestUserStore:
 
 class TestRateLimiter:
     def test_initial_state(self):
-        from backend.ratelimit import is_rate_limited, get_status
+        from backend.ratelimit import get_status
         status = get_status("192.168.1.1")
         assert status["limited"] is False
         assert status["failures"] == 0
@@ -268,7 +262,6 @@ class TestRateLimiter:
 class TestMiddleware:
     def test_is_auth_enabled_logic(self):
         """is_auth_enabled reads OBSIGATE_AUTH_ENABLED env var."""
-        import os
         from backend.auth.middleware import is_auth_enabled
         # The function checks if env var != 'false'
         # In our test env it may be set by fixture — test the logic