create --type addition
add: node-scoped update notifs — what updated, when, old → new, changelog link
Milestone body item (releases#331): node-scoped notifs which divulge WHAT was updated + WHEN (HH:MM[AM|PM] YYYY-MM-DD, local) + old version + new version + changelog link.

Today an applied update leaves only `ReleaseCache::record_last_outcome` (one overwritten string) and the now-signal `<UPDATES>` block carries versions only; nothing tells a session that something changed, from what, or where to read about it.

Ask: every apply — operator-run or background — emits one notif row per subject (spt-core, each adapter) on the existing primitive (ADR-0046): scope `node`, coalesce key `update:<subject>` (latest wins), body `UPDATED <subject> <old> → <new> at <HH:MMAM|PM YYYY-MM-DD> — changelog: <url>`. The core link is the node-prefixed served changelog (`…/<node>/docs/changelog.html`); an adapter's link rides only when its manifest declares `changelog` (sibling request) and points at the served adapter page. Background applies of an adapter also carry that adapter's `[update].message` / post-step notice in the same row, so `/reload-plugins`-class actions reach sessions (the minimal seam of releases#4, which stays deferred). `spt update status` prints the same last-applied line per subject.

Gate: unit on body rendering (12h clock, local tz, link presence rules); int: an apply on the two-daemon rig lands the row at scope node, coalesced on a second apply.