feat(agent-inbox): add popup queue of agents that need you

[JacobAtchley]

Summary

New jacob.agent-inbox plugin: a popup listing agents that need you, with quick replies so you can work through them without switching panes.

• Blocked agents come first, then done ones. Within each group, the agent whose state changed longest ago is on top. Working agents are listed underneath.
• Each blocked or done agent shows one line of context: the blocked agent's question, or the first line of the done agent's last message. If neither is found in the pane, the session title is shown.
• Keys:
  • enter jumps to the agent.
  • On a blocked agent, y presses Enter (the dialog's highlighted "yes") and n presses Escape.
  • On a done agent, c sends "continue" and r opens a reply prompt.
• After a quick reply, the agent stays hidden until herdr reports a new state for it.
• The list refreshes every second while the popup is open.
• herdr-client: Agent gains state_change_seq and title (terminal_title_stripped), both optional.

herdr does not report when a state started, so rows show no wait time. The order comes from the state change counter.

Test plan

• just ci (fmt, clippy with warnings denied, all workspace tests)
• Unit tests: ordering, location labels, preview extraction, key handling, reply mode, hiding answered agents, rendering and scrolling
• enter/esc key names accepted by herdr's send_keys
• Opened from a keybinding in herdr and used against live agents

🤖 Generated with Claude Code

https://claude.ai/code/session_015nTj3MJJCLb6JoXjRYeoxq

[enesccinar]

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