Add scoped calculate analytics endpoint

[anth-volk]

Fixes #1501

Summary

• Add GET /analytics/calculate/requests for value-free calculate request analytics.
• Support optional start_time/end_time filters and unique=true variable-key aggregation.
• Require the read:calculate-analytics scope for the analytics endpoint only.
• Wire static test-token scopes through config and CI token fetching.
• Document the endpoint and schemas in OpenAPI.

Testing

• uv run pytest -q tests/unit/decorators/test_auth.py tests/unit/endpoints/test_analytics.py
• uv run pytest -q tests/unit/utils/test_config_loader.py::TestEnvironmentVariableOverrides::test__given_traditional_env_vars__config_maps_them_correctly tests/unit/utils/test_config_loader.py::TestEnvironmentVariableSubstitution::test__given_auth0_config_with_env_vars__substitution_enables_auth tests/unit/utils/test_config_loader.py::TestConfigValueSettings::test__integration_with_real_config_structure
• uv run ruff check policyengine_household_api/decorators/auth.py policyengine_household_api/api.py policyengine_household_api/utils/config_loader.py tests/conftest.py tests/fixtures/decorators/auth.py tests/unit/decorators/test_auth.py tests/fixtures/endpoints/analytics.py tests/unit/endpoints/test_analytics.py
• uv run ruff format --check policyengine_household_api/decorators/auth.py policyengine_household_api/api.py policyengine_household_api/utils/config_loader.py tests/conftest.py tests/fixtures/decorators/auth.py tests/unit/decorators/test_auth.py tests/fixtures/endpoints/analytics.py tests/unit/endpoints/test_analytics.py
• uv run python -c "import yaml; yaml.safe_load(open('policyengine_household_api/openapi_spec.yaml'))"

Manual setup

• Auth0 Household API audience needs read:calculate-analytics.
• Grant that scope only to internal/admin clients.
• GitHub secret AUTH0_TEST_TOKEN_SCOPES should be set to read:calculate-analytics where scoped token fetching is needed.