Loop canary: document notification smoke path

[Svaag]

This is a low-risk Engineering Loop production canary.

Scope:

• Add or update a short documentation note under docs/engineering-loop/ describing the production loop notification smoke path: each daemon cycle reports status to Discord and submits the loop!engineering-loop passive check to Icinga.
• Documentation only.

Constraints:

• Do not change code, tests, workflows, secrets, runtime config, or Ansible.
• Touch docs/ only.
• Publish a draft PR only; humans still review/merge.

Acceptance:

• A draft PR exists for this issue.
• The PR only changes documentation under docs/.

[Svaag]

Production Engineering Loop canary succeeded. The loop loaded Knowledge MCP context (knowledge_context_status=ok), published draft PR #21, and reported both Discord and Icinga notification success. Removing loop:approved to prevent duplicate timer runs while the draft PR awaits human review.