fix(ci): load E2E role from Secrets Manager

[Hweinstock]

Summary

• Fetch E2E_AWS_ROLE_ARN from Secrets Manager inside each E2E matrix job.
• Pass the fetched value to aws-actions/configure-aws-credentials@v6.
• Clear the reader-role credentials before assuming the E2E execution role.
• Remove the dependency on the unverified vars.E2E_ROLE_ARN configuration.

This mirrors the established main E2E workflow.

Resulting flow

authorize job
  -> assume workflow Secrets Manager reader role
  -> fetch AUTHORIZED_USERS
  -> output is-authorized=true|false

each authorized E2E matrix job
  -> assume workflow Secrets Manager reader role
  -> fetch E2E_AWS_ROLE_ARN
  -> configure-aws-credentials assumes that E2E role
  -> run tests with temporary E2E credentials

GitHub matrix jobs do not share process environments, so Linux, Windows, and macOS each fetch the role ARN independently.

Evidence

The shared workflow previously used:

role-to-assume: ${{ vars.E2E_ROLE_ARN }}

E2E_ROLE_ARN is not defined as a repository variable or as an e2e-testing environment variable. Organization-variable visibility requires organization-admin permission, so its availability could not be verified.

The established main workflow instead fetches E2E_AWS_ROLE_ARN with the same pinned fetch-secrets action and then uses:

role-to-assume: ${{ env.E2E_AWS_ROLE_ARN }}
unset-current-credentials: true

This PR adopts that known path.

Separate IAM prerequisite

The original failing e2e / authorize job failed before E2E-role retrieval because the workflow Secrets Manager reader role did not trust the refactor branch's OIDC subject. This code change does not broaden that role's trust policy; the reader role must permit every branch or environment expected to call fetch-secrets.

Validation

• Workflow YAML parsed and structural assertions passed
• bunx prettier --check .github/workflows/e2e-test.yml
• bun run lint:check
• bun run typecheck
• bun run build
• git diff --check
• The same implementation shape received independent review with no blocking findings