feat(coding-agent): prioritize active agents in Agent Hub

[wolfiesch]

What

• Default Agent Hub to an Active dashboard that shows running agents and collapses idle agents behind an explicit disclosure row.
• Move parked, aborted, and advisor history into an Archive tab.
• Add a responsive selected-agent inspector for runtime capabilities, usage, retry state, current activity, and recent tools.
• Keep focus, transcript, revive, kill, collaboration, and persisted-transcript behavior explicit per tab.

Why

Long-lived sessions accumulate reusable and historical agents, causing stale rows to crowd out work that is running now. The new split keeps current work visible while retaining archived transcripts and lifecycle controls.

Testing

bun test packages/coding-agent/test/agent-hub-ordering.test.ts packages/coding-agent/test/agent-hub-activate.test.ts packages/coding-agent/test/agent-hub-advisor-scroll.test.ts packages/coding-agent/test/agent-hub-dashboard.test.ts packages/coding-agent/test/issue-2750-subagent-runtime-fallback.test.ts
bun check

Screenshots

Live Agent Hub with two running subagents.

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• bun check passes
• Tested locally
• CHANGELOG updated (if user-facing)