fix(search,graph): M4b wiki/entities/ → tier=knowledge

Initial M4 mapping put wiki/entities/* in tier=note. Post-M4 eval
regressed qwen35-9b-fast from rank 2 → off top-5: knowledge entries
that cite the entity in passing now outscore the entity page itself
(1.5× weight vs 1.0×).

Entity anchor pages are durable facts about concrete things — they
map cleanly to the knowledge/facts/ slot in the post-M3 layout
target. Promote them now so the path inference matches.

Eval re-run after deploy is in infra#72.

ingestion/internal/search/search.go

@@ -343,6 +343,11 @@ func extractTier(content, relPath string) string {
 	case "notes":
 		return "note"
 	case "wiki":
+		// wiki/entities/ anchor pages map to knowledge (see
+		// graph.inferTierFromPath for the rationale).
+		if len(parts) >= 2 && parts[1] == "entities" {
+			return "knowledge"
+		}
 		return "note"
 	case "knowledge":
 		return "knowledge"