The terminal lists the crew's agents with model, brief and budget, and an admin changes one after a plan, as MCP `agent` does #7289

For: the owner tuning the crew from the terminal: a cheaper model here, a tighter budget there. Steering means the crew's settings are where the owner works.

createAgent, updateAgent and deleteAgent are reached from /api/v1/agents and MCP agent (src/http/mcp/tools/agent.ts). The terminal has a teams screen but no agents screen.

Done:

• [ ] A new src/tui/screens/agents.ts, opened from the palette in src/tui/forge.ts as "Crew agents" for an admin who is a person. Each row: username, model, budget and the first line of the brief.
• [ ] m, b and B change model, budget and brief; each shows the plan and applies only after a confirm, through updateAgent, refused in MCP's words when out of bounds.
• [ ] n creates one (username, then model) and d removes one after a confirm.
• [ ] A new test/tui-agents.test.ts: list, change a budget after a confirm, refuse a bad model, create and remove one; a non-admin is never offered the screen.

Files: src/tui/screens/agents.ts, src/tui/forge.ts, one test. Risk: medium; removing an agent is not undoable, so the confirm names it.