Isolate non-blocking managed-config CI

[lilly-luo]

Summary

• move the experimental managed-config matrix out of the required reusable Integration workflow
• run it as an independent, non-blocking top-level workflow on PRs, main, and manual dispatch
• preserve the same tests, versions, credentials, artifacts, timeout, and continue-on-error behavior

Hypothesis

A hosted-runner shutdown produces a cancelled job, which continue-on-error does not absorb. When that job is part of the reusable Integration workflow, cancellation poisons the required e2e gate. An independent workflow contains cancellation without hiding its signal.

Validation

• git diff --check
• CI on this PR is the behavioral validation: required CI/Integration must complete independently of the managed-config workflow.