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/lib.rs

@@ -50,6 +50,6 @@ pub use stores::{
     approvals, audit_log, broker, build_logs, db, operator_questions, power, scheduled_prompts,
 };
 pub use workers::{
-    agent_sockets, auto_update, crash_watch, knowledge, reminder_scheduler,
+    agent_sockets, auto_update, crash_watch, knowledge, mcp_sockets, reminder_scheduler,
     scheduled_prompts_worker,
 };