create --type addition
add: manifest `[adapter] summary` + `changelog` fields — changelog rendered at install, served at the adapter's node-prefixed page
Milestone body item (releases#331): if an adapter manifest designates a changelog doc, its core-hosted URL is linked everywhere that adapter's updates are divulged (notif and CLI output).

Today `[adapter]` has name/kind/version/min_spt_core_version/hostable_types/shortcut_basename/web_short_path/docs_dir/host_binaries — no summary, no changelog (manifest.rs ~208-252). No markdown renderer exists in the tree; mdbook is release-side tooling.

Ask (ruled grill 2026-09-24): two optional `[adapter]` fields — `summary` (one plain paragraph, ≤300 chars) and `changelog` (archive-relative markdown path). At `adapter add`/`update` the CLI renders the changelog markdown → HTML with `pulldown-cmark` (one small pure-Rust dep, justified) into a `changelog.html` sidecar in the install dir; the daemon stays a byte-server. Served at `http://localhost:5474/<node>/a/<adapter>/changelog` (node-prefixed, proxied cross-node like every served resource). That URL is the link `spt adapter update` output, `spt update status`, and the update notif (releases#337) carry; absent the field, no link and no claim. The docs-nav page (releases#332) consumes the same sidecar + summary. MANIFEST.md + manifest.schema.json updated in the same change; the fields are additive (older adapters unaffected).

Gate: unit on field parsing + schema; int: install a mock adapter declaring both, GET the page, assert rendered HTML; a mock without the fields 404s the page and prints no link.