docs: add CloudShell FOG integration note (v2 draft)

[mdheller]

Summary

Adds the TurtleTerm-side CloudShell FOG integration note on a fresh branch from current main and preserves the current receipt-context smoke test surface.

Included

• docs/integration/cloudshell-fog.md
• current-main-compatible generated RPM builder fix so generated RPM %install invokes the staging helper through bash

Why this supersedes older PRs

Earlier integration branches diverged while main absorbed bridge wrappers, receipt-context smoke testing, and sibling-path wrapper fixes. This v2 branch starts from current main and carries only the minimal remaining delta.

Follow-up tracking

Repo-wide packaging/security checks remain tracked separately if still failing:

• native Linux package verification: Stabilize native package build verification for RPM/Debian/Arch #7
• cargo-audit posture: Classify and remediate cargo-audit findings #8
• Homebrew install-from-HEAD validation: Stabilize Homebrew install-from-HEAD validation #9