swarm: show subagent terminals in the swarm UI

An agent's subagent daemon publishes each subagent's output as terminal
rows on `$SWARM.term.<agent>.sub.<subagent>`, as the agent, into a
per-agent stream it creates itself; swarm-controller lists an agent's
subagents from that stream's subjects and relays one subagent's rows as
SSE; the swarm UI lists them under the agent's terminal preview and
reuses AgentTermPreview, full-screen tab included, with no input.

- swarm-nats.nix: the agent token may also publish
  `$SWARM.term.{agent}.sub.>` and `$JS.API.STREAM.CREATE|INFO` on
  `term-sub-{agent}`, and nothing else of JetStream. A module-eval arm
  pins the agent-token grant as an exact list.
- mcp.nix: hive-subagent-daemon loads the agent's store identity
  (`hive-agent-bao-cert/-key/-server-ca`, the ones hive-agent loads)
  whenever the agent has a store, not only on the opencode preset. The
  agent's own queue secret lives in the store, so this is the credential
  the harness connects with.
- hive-subagent-mcp: `swarm_term` reads the agent's queue secret under
  that identity, connects with the agent token, opens or creates
  `term-sub-<agent>` (max_age 24h), and publishes classified rows from
  the sink every subagent line already passes through. The sink only
  queues (bounded, drop-and-count); a missing store, refused credential,
  failed stream create or failed publish is a log line.
- The stream-json classifier (`stream_enrich`) and the `TermMsg` row
  types plus `fit` move from the hive-agent binary into hive-sh4re, so
  the subagent daemon publishes the rows AgentTermPreview already
  renders. hive-agent keeps its LiveEvent classifier on top.
- swarm-controller: `GET /api/agents/{name}/subagents` and
  `GET /api/agents/{name}/subagents/{subagent}/term/stream`.
- docs/swarm: what the UI shows and what the queue carries.

Closes #4827

swarm-queue-client/src/lib.rs

@@ -125,6 +125,15 @@ pub enum Error {
         #[source]
         source: async_nats::jetstream::context::CreateStreamError,
     },
+
+    #[cfg(feature = "subagent-term")]
+    #[error("creating the {stream} stream")]
+    CreateAgentStream {
+        // Owned: the name carries the agent's (`subagent_term::stream_name`).
+        stream: String,
+        #[source]
+        source: async_nats::jetstream::context::CreateStreamError,
+    },
 }
 
 /// Render an error and its source chain on one line.
@@ -248,6 +257,11 @@ pub struct DeployRequest {
 #[cfg(feature = "notices")]
 pub mod notices;
 
+/// The subject an agent's subagents' terminal rows go to, and the per-agent
+/// stream that lists them. Only opening the stream needs the `subagent-term`
+/// feature; the names are unconditional, like [`agent_icon`]'s.
+pub mod subagent_term;
+
 /// Only the fields this needs; authelia returns several.
 #[derive(serde::Deserialize)]
 struct TokenResponse {