feat(#2290): split ensure_runtime — dirs to lifecycle, listeners to mcp_sockets supervisor

- lifecycle::ensure_agent_runtime_dir(name): pure filesystem op, no
  Coordinator dep. Creates /run/hyperhive/agents/<name> without touching
  the MCP listener map.

- workers/mcp_sockets::spawn_poll(coord): 10 s reconcile loop (same shape
  as agent_sockets::spawn_poll). Converges 'agent running => MCP listener
  bound'. First tick is immediate so hive-c0re restarts re-register all
  running agents without waiting a full interval. Fixes the dead-listener-
  after-daemon-restart gap.

- All ensure_runtime() call sites updated:
  - Prebuild/Swap/WriteDropin: Coordinator::agent_dir() (pure, no IO)
  - Reconcile-Start: ensure_agent_runtime_dir + agent_dir (dir may be
    missing after reboot; listener deferred to supervisor)
  - run_create / handle_spawn: ensure_agent_runtime_dir + register_agent
    (eager on first spawn so socket ready before harness first turn)
  - apply_commit / merge_config_pr: ensure_agent_runtime_dir + agent_dir
  - Manager (auto_update): ensure_agent_runtime_dir + agent_dir
    (manager has no MCP listener; socket_server::start_manager owns it)

- ensure_runtime() retained in Coordinator with updated doc pointing at
  the preferred split form. No callers remain outside tests.

hive-c0re/src/workers/mod.rs

@@ -1,12 +1,13 @@
 //! Background tasks and periodic sweeps: crash/login watcher, the
 //! reminder and scheduled-prompt delivery loops, boot-time auto-update
-//! reconcile, the agent-sockets.json writer loop, and knowledge-repo
-//! sync. Each submodule is re-exported at the crate root, so
-//! `crate::crash_watch::…` etc. keep working unchanged.
+//! reconcile, the agent-sockets.json writer loop, the MCP socket listener
+//! reconcile loop, and knowledge-repo sync. Each submodule is re-exported
+//! at the crate root, so `crate::crash_watch::…` etc. keep working unchanged.
 
 pub mod agent_sockets;
 pub mod auto_update;
 pub mod crash_watch;
 pub mod knowledge;
+pub mod mcp_sockets;
 pub mod reminder_scheduler;
 pub mod scheduled_prompts_worker;