over-engineering audit: remove dead code, speculative config, duplicate queues

- delete embedded community resolver snapshot (6,760 lines) + EmbeddedServers +
  DNS_SERVERS=fresh; curated resolvers are the default. Simplify Warm (no
  sampling).
- one generic internal/sample.Queue[T] replaces three near-identical
  random-sample queues (probe, pipeline, discover).
- delete unreachable index.listOpenSearch (OpenSearch is never listable).
- delete classifyCloudFront (its match is always discarded, !ResourceSpecific).
- delete probe.Probe wrapper + Describe; tests use ProbeDetailed.
- delete store.Pool(), model.SourceDNSAlias, discover.QueueLen.
- drop dead config/no-op knobs: pipeline DirectWorkers, discover MaxPerDomain,
  discover S3/GCS/DO flags, BUCKET_SCAN_DO.
~-7,000 lines (mostly the resolver snapshot), 0 deps removed, tests green.

internal/pipeline/pipeline_test.go

@@ -269,7 +269,7 @@ func TestDNSDedup(t *testing.T) {
 	p := New(Config{DNSQueueSize: 8, Metrics: m})
 	p.HandleHost("files.example.com")
 	p.HandleHost("files.example.com")
-	if got := p.dnsQ.len(); got != 1 {
+	if got := p.dnsQ.Len(); got != 1 {
 		t.Fatalf("dns queue len = %d, want 1", got)
 	}
 }