Extract `unarchiveAgentState` and `sendPromptToAgent` into `mcp-shared`
so every surface (app/WS, MCP, CLI-through-MCP) runs the same sequence:
unarchive → ensureAgentLoaded → optional mode change → recordUserMessage
→ startAgentRun. MCP `send_agent_prompt` previously skipped unarchive and
cold-agent rehydration, so sending to an archived agent over MCP left it
hidden from `paseo ls` and failed entirely when the agent wasn't already
in memory. Session now delegates to the shared function and its private
`unarchiveAgentState` is gone.
Mohamed Boudra
a11c246bdc