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/index/index_test.go

@@ -81,19 +81,6 @@ func TestListFirebase(t *testing.T) {
 	}
 }
 
-func TestListOpenSearch(t *testing.T) {
-	x, host := newTestIndexer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
-		_, _ = w.Write([]byte(`[{"index":"logs-2024","docs.count":"100","store.size":"1.2mb"}]`))
-	}))
-	entries, err := x.List(context.Background(), model.Candidate{Hostname: host, Provider: model.ProviderAWS, Service: model.ServiceOpenSearch})
-	if err != nil {
-		t.Fatal(err)
-	}
-	if len(entries) != 1 || entries[0].Name != "logs-2024" || entries[0].Size != 100 {
-		t.Fatalf("unexpected entries: %+v", entries)
-	}
-}
-
 func TestListBounded(t *testing.T) {
 	var keys strings.Builder
 	for i := 0; i < 100; i++ {