test(indexer): created event emits notification

[Bhargi777]

Closes #151

Summary

• Cover the stream_created webhook notification emitted by a created donation-vault event.
• Assert the event ID, stream ID, donor address, and resolved NGO ID in the JSON payload.
• Restore webhook environment and fetch mocks after the test.

Validation

• git diff --check and targeted Prettier check passed.
• npm run lint passed.
• npm run typecheck is blocked by the existing origin/main missing @fastify/compress dependency.
• Integration test execution requires PostgreSQL; this environment has no Docker/Postgres service.