ci: post auto-merged PRs to Discord #loop-live

[nwnwnw413]

Adds a GitHub Actions workflow that posts a one-line notice to the Chrono AI Discord #loop-live feed whenever the consensus loop auto-merges a PR in this fork.

What it does

• Triggers on pull_request: closed, runs only when merged == true and the PR carries the crnd:human:auto label (i.e. loop-merged PRs only).
• Posts ✅ Auto-merged PR #N — <title> to #loop-live via the NyxID proxy (/proxy/s/chronoai-bot-1738). The Discord bot token is injected by NyxID, never stored here.

Why a workflow (not a change to the loop engine)

• The merge/comment logic lives in consensus-rnd. This keeps that repo untouched: the feed is driven entirely from inside this fork, firing on the merge event GitHub already emits.

Required setup (one secret)

• Add repo secret NYX_DISCORD_KEY = a NyxID agent key scoped to the chronoai-bot service.
• No-op until the secret is set, so this PR is safe to merge before the key exists.

Channel: #loop-live (1518548271277281290) in the Chrono AI production server.