[Feature] Show Prime Agent RLM subagent status and parent-child hierarchy

[lsvab]

Problem

GooeyPi does not show when Prime Agent RLM subagents are running.

When the parent agent finishes its own turn but one or more child agents are
still working, the parent session can appear idle or finished in GooeyPi.
This makes it difficult to know whether the overall task is complete.

Subagent completion or cancellation may only appear later as a raw transcript
message, for example:

RLM child ... was cancelled: Deleted by parent orchestrator

There is currently no visible list, running count, or parent-child hierarchy.

Expected behavior

GooeyPi should provide a visible subagent status display for Prime Agent
sessions. For example:

• Show the number of running subagents next to the parent session.
• Keep the parent session marked as working while it has running children.
• Provide an expandable parent-child agent tree.
• Show each subagent's name and state:
  • starting
  • running
  • completed
  • failed
  • cancelled
• Show a clear notification when all child agents have finished.
• Replace raw lifecycle messages with user-friendly status messages where
  appropriate.

Available Prime Agent data

prime-agent list --all --json already exposes useful fields such as:

• runtimeKind
• parentSessionId
• parentSessionPath
• rlmChildId
• rlmDepth
• rosterStatus
• hasRunningRlmChildren
• isSessionActive
• isStreaming

This appears to provide enough information to build the hierarchy and status
indicators without parsing the child transcripts directly.

Environment

• GooeyPi: 1.1.16
• Prime Agent: 0.9.3
• Platform: Linux x64

Suggested acceptance criteria

1. A parent session shows a running-child count.
2. A parent remains visually active while hasRunningRlmChildren is true.
3. Users can expand the parent session to inspect its child agents.
4. Child status changes appear without manually refreshing the application.
5. Completion, failure, and cancellation are clearly distinguishable.