archetypes: prefill the create form from flake-declared agent archetypes

A flake declares agent archetypes in its `hyperhiveArchetypes` output,
`<name> = { module; meta; }`. The hyperhive flake ships `reviewer`
(default permissions without `execution`).

swarm-builder answers `$SWARM.builder.archetypes` with the `meta` of
every archetype its own hyperhive source declares. swarm-controller asks
once the queue connects and every 10 minutes, checks each archetype as
`POST /api/agents` checks its settings, and stores the result in the
`agent-archetypes` KV bucket when it changed. `GET /api/archetypes`
serves it, and the create form's archetype select prefills permissions,
resource caps and inference from it.

The agent created is an ordinary agent with its own config repo; the
archetype's module is not applied yet.

Refs #5386

docs/README.md

@@ -91,6 +91,8 @@ declarations.
   (planned, not implemented yet).
 - **Does an agent config PR build before it's merged?** →
   [`swarm/builder.md`](swarm/builder.md).
+- **How do I create an agent from a ready-made set of permissions and
+  settings?** → [`swarm/archetypes.md`](swarm/archetypes.md).
 - **How long do CI runs take, per repo and PR, and where does the board get
   it?** → [`swarm/ci-metrics.md`](swarm/ci-metrics.md).
 - **How do I log an agent in to claude from the swarm UI, and why doesn't a