Subagents in the CLI (harness spec 3.3.0): the model, capacity, the offer, /context

- A task subagent or a team member runs on the session's model unless the
  person named another in this session's own messages (team/subagents.ts;
  engine.personSaid reads every prompt and mid-turn message, compacted ones
  included). Not named: refused; an agent file's own model is not used.
- Another model on the session's one-model server is refused; a one-request
  session model is not its own subagent, and nothing else is picked.
- The team is offered when a model could serve: the session's with two
  slots, or any usable model off its one-model server; the size note adds
  team_own when the session's model cannot serve its own.
- "Subagents" in /effort, /team, /settings and the config schema; the status
  bar reads "agents 3/4 · 2 subagents working".
- /context: used of the window, one bar by category, each category's share,
  what is free, and "N until auto-compact".
- Conformance runner for the subagents area (26 cases); helper -> task.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

tests/acp-jobs.test.ts

@@ -151,7 +151,7 @@ test("a background subagent: its transcript as history turns; send to a finished
   ], { route: (model) => (model.startsWith("g/") ? child : undefined) })
   config(fake.url, true)
   const { c, events, sid } = await client()
-  await c.request("session/prompt", { sessionId: sid, prompt: [{ type: "text", text: "go" }] })
+  await c.request("session/prompt", { sessionId: sid, prompt: [{ type: "text", text: "go (a subagent on g/m)" }] })
   expect(await until(() => events.some((e) => e.type === "job" && e.state === "end"))).toBe(true)
   const listed: any = await c.request("_lembas/jobs", { sessionId: sid })
   expect(listed.jobs[0]).toMatchObject({ id: "job1", kind: "subagent", state: "done", agent: "explore", description: "find the bug", model: "g/m" })