feature: add push functionality for agents or hands to send messages to channels

[9M6]

Description

As title describes, the ability for the agents to send messages to the user asynchronously, let say a hand operates every N amount of time, after writing/finalizing should send it to one or all channels the agent is connected.

Alternatives Considered

There's no alternatives

Additional Context

Agents should be pull/push

[jaberjaber23]

Proactive messaging is already supported. Agents can send messages to channels via the channel_send tool, and cron jobs can trigger agent turns on a schedule which then respond to configured channels. The cron system supports periodic agent_turn actions that can include instructions like "send a status update to the telegram channel." Hands also run on schedules and can output to channels. The webhook system (/hooks/agent) allows external systems to trigger agent actions with channel output.