Seed relay: dead NNTP connections found in 90 s and retried

Five ranges "never answered" in 10 minutes, yet their chunk came back in
0.3 s on a fresh connection: the news server drops idle connections
without telling, and the pool's next request on one waited for the
10-minute inactivity timeout. Now: SEED_NNTP_TIMEOUT_MS 90 s (inactivity;
slow ranges keep streaming), one retry on a fresh connection, and pooled
connections idle over 60 s are replaced before use.

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

lib/nntp/xover_client.ts

@@ -10,7 +10,7 @@ export interface XoverClientOptions {
   secure?: boolean
   /** Hostname the TLS certificate must match, when connecting through a tunnel (default: host). */
   servername?: string
-  /** A command whose reply stalls this long fails, and the connection with it. */
+  /** A reply with no data for this long fails, and the connection with it (inactivity, not duration). */
   timeoutMs?: number
   /** Ask for gzip-compressed overview data (XFEATURE COMPRESS GZIP), when the server has it. */
   compress?: boolean