Close NNTP connections left idle for NNTP_IDLE_CLOSE_SECONDS

Eweka drops quiet connections, so the next command on one failed
("Spot inspection failed: NNTP connection closed"), and idle connections
held account slots that downloads could use. The coordinator pool now
closes free connections (and the plain one) on its sync once idle for
60 s; dry prober lanes, the spotter between rounds and the spot inspector
with nothing to inspect close theirs too, reconnecting when work comes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

config/coordinator.ts

@@ -81,6 +81,13 @@ export default {
    * under 2 minutes old as on ones over 10 (~25–35%; LOG.md 2026-10-09 (16)).
    */
   nntpConnectionMaxMs: env.get('NNTP_CONNECTION_MAX_MINUTES', 0) * 60 * 1000,
+  /**
+   * A connection with nothing to do for this long is closed, and opened again
+   * when there's work. 0: kept. Eweka drops connections that stay quiet, and
+   * the next command on one failed ("Spot inspection failed: NNTP connection
+   * closed"); idle ones also take the account's connections from downloads.
+   */
+  nntpIdleCloseMs: env.get('NNTP_IDLE_CLOSE_SECONDS', 60) * 1000,
   probe: {
     /**
      * At most (its share, nntpShares): NNTP connections the prober reads articles with, besides the