nudge.py: drop host filter and queue-path cooldown

scr-agent-inbox-nudge.py queue path: (a) drop ?host= from the /unread_agents query - the script only ever acts on tmux panes on its own host, and the pane enumeration plus the codex environ identity check (queue_push :495) already bind the target to this host; the host filter is an optimization that turns into invisibility when roster.host is blank or wrong (known: NULL host hides an agent). (b) COOLDOWN=180 is a keystroke-spam guard inherited from send-keys and is dead weight on the queue path: a queued message is persisted, not typed, so there is nothing to spam. Measured 2026-09-22: it held coder-llmmsgsrv-cc's DM 130261 for 127s. Apply COOLDOWN to the send-keys fallback only. PERSIST_SECS=20 stays (or shortens to one tick): it is the window for the agent's own shim to drain first; a duplicate is the cost of shortening it, a loss is not.