feat(server): INGEST_WING_RESOLVE=1 wires the wing resolver into the watcher (#205 S3)

Off by default (retired layout unchanged). On: eligibility from
classification.yaml, local ingest LLM as classifier, BM25 as cross-check,
INGEST_WING_THRESHOLD (default 0.9, rejected outside [0,1]). Build failure
is fatal when explicitly enabled.

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

ingestion/internal/wing/known.go

@@ -0,0 +1,39 @@
+package wing
+
+import (
+	"fmt"
+	"os"
+	"path/filepath"
+	"sort"
+)
+
+// legacyDirs are the retired wiki/{concepts,entities,sources}/ layout, not wings.
+var legacyDirs = map[string]bool{"concepts": true, "entities": true, "sources": true}
+
+// KnownWings lists wiki/<wing>/ directories that contain at least one hall
+// subdirectory, sorted. The retired layout is not a wing. A missing wiki/ is
+// an error: an unreadable brain must not look like "no wings".
+func KnownWings(brainDir string) ([]string, error) {
+	entries, err := os.ReadDir(filepath.Join(brainDir, "wiki"))
+	if err != nil {
+		return nil, fmt.Errorf("list wings: %w", err)
+	}
+	var out []string
+	for _, e := range entries {
+		if !e.IsDir() || legacyDirs[e.Name()] {
+			continue
+		}
+		subs, err := os.ReadDir(filepath.Join(brainDir, "wiki", e.Name()))
+		if err != nil {
+			continue
+		}
+		for _, s := range subs {
+			if s.IsDir() {
+				out = append(out, e.Name())
+				break
+			}
+		}
+	}
+	sort.Strings(out)
+	return out, nil
+}