fix(docs): correct Pi Mono agents[] capability — adapter emits nothing for agent definitions

[espetro]

Problem

capability-matrix.md marks agents[] as ✅ on Pi Mono. The pimono adapter only handles hooks/commands/tools/shortcuts/flags — it does not emit anything for agents[] from the manifest.

subagentStart/subagentStop hooks DO correctly map to Pi's agent.AgentStart/agent.AgentStop events.

Acceptance criteria

• capability-matrix.md — agents[] Pi cell ✅ → ⚠️ with note: "Pi has no named-agent declaration; use nativeEntry.pimono for custom agent spawning"
• capability-matrix.md — subagentStart/subagentStop Pi cells keep ✅, add mechanism in Notes column: "maps to Pi agent.AgentStart/AgentStop lifecycle events"

Source

Plan: .agents/plans/2026-06-29-show-hn-launch-blockers.md — B2