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

hive-subagent-mcp/Cargo.toml

@@ -9,6 +9,8 @@ workspace = true
 
 [dependencies]
 anyhow.workspace = true
+# The swarm-queue client for publishing subagent terminals (`swarm_term`).
+async-nats.workspace = true
 axum.workspace = true
 clap.workspace = true
 hive-agent-sock.workspace = true
@@ -17,6 +19,7 @@ hive-runtime.workspace = true
 # `permissions::builtin_tools_arg` — the same `--tools` resolution the parent
 # harness spawns its own claude with, so a subagent's built-in surface is its
 # parent's rather than a second list that drifts. See `session::build_config`.
+# Also `term_msg`/`stream_enrich`, the rows `swarm_term` publishes.
 hive-sh4re.workspace = true
 hive-sock-client.workspace = true
 hive-types.workspace = true
@@ -25,6 +28,10 @@ rmcp.workspace = true
 schemars.workspace = true
 serde.workspace = true
 serde_json.workspace = true
+# `subagent_term`: the subject, the stream, and opening it as the agent.
+swarm-queue-client = { workspace = true, features = ["subagent-term"] }
+# The agent's own queue credential, read under its store identity.
+swarm-secret-client.workspace = true
 tokio.workspace = true
 tracing.workspace = true
 tracing-subscriber.workspace = true