Refresh test user passwords after DB resets

[karilint]

Motivation

• Ensure API tests can log in after a test database reset by recreating or updating test user accounts with known credentials.

Description

• Call test/create-test-users from resetDatabase in backend/src/api-tests/utils.ts so test users are (re)created after database resets.
• Update createTestUsers in backend/src/services/user.ts to update existing accounts by setting newpassword and now_user_group so passwords and roles are refreshed for preexisting users.
• Remove an obsolete API test file (src/api-tests/species/create.test.ts) that was deleted in the diff.

Testing

• Ran npm run lint and the linter completed successfully.
• Ran npm run tsc and TypeScript compilation completed successfully.
• API tests (npm run test:api:local) were not executed as part of this rollout because they require a configured test database and environment.

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Codex Task