Defensively unset env vars in all integration tests and fix API context

[google-labs-jules]

• Integration Test Hardening: Updated all tests in pkg/app and pkg/bot to explicitly UnsetEnv for BIBLE_API_URL and BIBLE_API_KEY. This ensures that tests running in CI (where GCLOUD_PROJECT_ID is set) strictly use Google Secret Manager and do not accidentally pick up environment variables.
• API Client Test Fix: Updated TestSubmitQuery to use a Verses query (avoiding flaky LLM endpoints) and populated QueryContext with a valid Version to prevent API bad request errors.
• Test Utils: Exported SetEnv and UnsetEnv in pkg/app/test_utils.go for use across packages.

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PR created automatically by Jules for task 535107038277093355 started by @julwrites

[google-labs-jules]

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