Seed relay: compressed overviews by default again

Measured with 20 relay connections, plain and gzip both gave ~1.5 chunks/s
for 2026 a.b.ath articles; plain used many times the CPU and traffic.

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

tests/unit/seed_fetch_pool.spec.ts

@@ -27,7 +27,7 @@ test.group('SeedFetchPool', () => {
     })
     await new Promise<void>((resolve) => server.listen(0, '127.0.0.1', resolve))
     const saved = { host: nntpConfig.host, port: nntpConfig.port, secure: nntpConfig.secure, connections: indexerConfig.seed.nntpConnections, compress: indexerConfig.seed.nntpCompress }
-    // The fallback from a compressed pooled connection (SEED_NNTP_COMPRESS on).
+    // The fallback from a compressed pooled connection (the default).
     indexerConfig.seed.nntpCompress = true
     Object.assign(nntpConfig, { host: '127.0.0.1', port: (server.address() as net.AddressInfo).port, secure: false })
     indexerConfig.seed.nntpConnections = 2