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/swarm/builder.md

@@ -61,6 +61,14 @@ Where it runs and how it's enabled: [`services.md`](services.md#builder).
   push. The jobs graph is in memory, so a controller restart drops a build in
   flight and leaves its status `pending`.
 
+## Archetype evaluation
+
+The builder also answers `$SWARM.builder.archetypes`: it evaluates the
+`meta` of every agent archetype its own hyperhive source declares, with no
+forge token, and answers with the JSON. An evaluation doesn't wait for a
+build in progress and has two minutes. What the controller does with the
+answer: [`archetypes.md`](archetypes.md).
+
 ## Credentials
 
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