Separate Boatstack workflow control plane

[bigboateng]

Summary

• keep Boatstack's CI and release workflows directly owned by this repository
• make CI support the current Python projection and automatically switch to the incoming Go helper on macOS, Linux, and Windows
• add the native helper release workflow for six OS/architecture targets
• leave the existing Intelligence Flow sync workflow unchanged

Why

Intelligence Flow now projects product/runtime content only. Boatstack's .github/workflows directory is a separate executable control plane and is never generated, overwritten, removed, or tracked by UPSTREAM.json.

This avoids custom sync tokens while keeping workflow changes visible as ordinary Boatstack PRs.

Merge order

1. Merge Separate Boatstack workflow ownership intelligence-flow#18.
2. Merge this control-plane PR.
3. Rerun Sync from Intelligence Flow to open the generated content PR.

Validation

• current Boatstack Python suite: 3 passed
• all three workflow files parse as YAML
• new CI preserves the legacy checks until boatstack/go.mod arrives, then selects Go tests/builds and installer validation