[codex] Isolate auth redirect URI test imports

[tianmind-studio]

Summary

• Stub optional jwt / jwt.algorithms.RSAAlgorithm import surfaces in test_auth_redirect_uri.py so the auth redirect tests collect in lightweight Windows backend environments.
• Add a temporary python_multipart stub while importing routers.auth, matching FastAPI's import-time Form route check without requiring the full multipart dependency for this test.
• Restore the real utils package path and ensure the Redis auth helper names exist when another stub-heavy test leaves lightweight package modules in sys.modules.

Root cause

test_auth_redirect_uri.py exercises redirect URI validation and auth-code binding, but importing routers.auth also imports optional Apple JWT helpers and builds FastAPI Form endpoints. In this Windows lightweight backend venv, standalone collection failed before any assertions ran:

ModuleNotFoundError: No module named 'jwt'

After the JWT stub, FastAPI's route construction also required python-multipart. Running after test_action_item_date_validation.py exposed a separate order dependency where that test leaves utils / database.redis_db stubs that do not satisfy routers.auth imports.

Validation

• python -m pytest backend/tests/unit/test_auth_redirect_uri.py --collect-only -q --tb=short -> 46 tests collected
• python -m pytest backend/tests/unit/test_auth_redirect_uri.py -q --tb=short -> 43 passed, 3 skipped
• python -m pytest backend/tests/unit/test_action_item_date_validation.py backend/tests/unit/test_auth_redirect_uri.py -q --tb=short -> 69 passed, 3 skipped
• python -m pytest backend/tests/unit/test_auth_redirect_uri.py backend/tests/unit/test_action_item_date_validation.py -q --tb=short -> 69 passed, 3 skipped
• black --line-length 120 --skip-string-normalization backend/tests/unit/test_auth_redirect_uri.py
• python -m py_compile backend/tests/unit/test_auth_redirect_uri.py
• git diff --check
• scripts/pre-commit