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/discover/discover_test.go

@@ -6,7 +6,7 @@ import (
 )
 
 func TestCandidatesAreExactLabelsOnly(t *testing.T) {
-	got := candidates("assets.example.com", 200)
+	got := candidates("assets.example.com")
 	if len(got) != 2 || got[0] != "assets" || got[1] != "example" {
 		t.Fatalf("candidates = %v, want [assets example] (no fabricated names)", got)
 	}
@@ -28,29 +28,21 @@ func TestBaseLabelsSkipsNoise(t *testing.T) {
 }
 
 func TestTargets(t *testing.T) {
-	d := New(Config{S3: true, GCS: true, DOSpaces: true, DORegions: []string{"nyc3"}})
+	d := New(Config{})
 	ts := d.targets("example")
-	if len(ts) != 3 {
-		t.Fatalf("got %d targets, want 3", len(ts))
+	if len(ts) != 2 {
+		t.Fatalf("got %d targets, want 2", len(ts))
 	}
-	var s3, gcs, do bool
+	var s3, gcs bool
 	for _, tg := range ts {
 		switch {
 		case strings.Contains(tg.URL, "example.s3.amazonaws.com/?list-type=2"):
 			s3 = true
 		case strings.Contains(tg.URL, "storage.googleapis.com/example"):
 			gcs = true
-		case strings.Contains(tg.URL, "example.nyc3.digitaloceanspaces.com/?list-type=2"):
-			do = true
 		}
 	}
-	if !s3 || !gcs || !do {
-		t.Fatalf("missing targets: s3=%v gcs=%v do=%v (%v)", s3, gcs, do, ts)
-	}
-}
-
-func TestMaxPerDomain(t *testing.T) {
-	if got := candidates("example.com", 5); len(got) > 5 {
-		t.Fatalf("MaxPerDomain not honored: got %d", len(got))
+	if !s3 || !gcs {
+		t.Fatalf("missing targets: s3=%v gcs=%v (%v)", s3, gcs, ts)
 	}
 }