chore: clean up pre-existing ruff violations in tests

Remove unused imports (F401) and strip trailing whitespace (W291/W293) flagged
by ruff in test files. Pre-existing debt unrelated to any single feature; CI runs
pytest but not ruff, so these had accumulated. No behavior change.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01NGzHtDvJur9U7ysgRKRUTN

tests/test_auth.py

@@ -12,10 +12,8 @@ import time
 import types
 
 import jwt
-import pytest
 from cryptography.hazmat.primitives.asymmetric import ed25519, rsa
 
-from intervals_mcp_server import auth as auth_mod
 from intervals_mcp_server.auth import AuthentikTokenVerifier, _audience_variants, build_auth
 
 ISSUER = "https://auth.example/application/o/x/"