* Fix chat everyone fanout
* Unify system-injected agent prompts
Chat mentions, schedule fires, and notifyOnFinish now share one shape:
prompt wrapped in <paseo-system>...</paseo-system>, no user-message
turn recorded, no auto-unarchive. Agents can recognize system-injected
context vs a real user turn.
- Move agent prompt orchestration out of mcp-shared.ts into a neutral
agent-prompt.ts module (mcp is an interface, not the home).
- Add `unarchive` and `recordUserMessage` flags to sendPromptToAgent.
- Add formatSystemNotificationPrompt helper.
- Schedule fires now identify themselves: "Schedule \"<name>\" fired
(id=..., run=...)." Plumb runId through runner so the paseo.schedule-run
label matches the actual run record.
- Replace chat-mention validateChatMentionFanout + duplicate
resolveChatMentionTargetAgentIds with single prepareChatMentionFanout
that owns expansion + cap + poster snapshot.
