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/dns/pool_test.go

@@ -30,15 +30,6 @@ func (f *fakeLookup) LookupIP(ctx context.Context, host string) ([]net.IP, error
 	return []net.IP{net.ParseIP("1.2.3.4")}, nil
 }
 
-func TestEmbeddedServers(t *testing.T) {
-	if n := len(EmbeddedServers()); n < 1000 {
-		t.Fatalf("embedded resolver list has %d entries, want thousands", n)
-	}
-	if n := len(CuratedServers()); n < 10 {
-		t.Fatalf("curated resolver list has %d entries, want at least 10", n)
-	}
-}
-
 func TestServerCooldown(t *testing.T) {
 	s := &server{}
 	now := time.Now().UnixNano()
@@ -86,7 +77,7 @@ func TestWarmDisablesDeadResolvers(t *testing.T) {
 	dead := &fakeLookup{ipErr: &net.DNSError{Err: "timeout", IsTimeout: true}}
 	deadServer := &server{r: dead}
 	p := &ServerPool{servers: []*server{deadServer, {r: good}}}
-	healthy := p.Warm(context.Background(), "example.com", 4, 0)
+	healthy := p.Warm(context.Background(), "example.com", 4)
 	if healthy != 1 {
 		t.Fatalf("healthy = %d, want 1", healthy)
 	}