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/graph/extract.go

@@ -99,11 +99,18 @@ func inferTierFromPath(e *Entity, docPath string) {
 	case "knowledge":
 		e.Tier = "knowledge"
 	case "wiki":
-		// Pre-M3 wiki layout: sources are synth output of raw inbox
-		// material (I tier); concepts + entities are reference notes
-		// (also I tier); top-level wiki/<slug>.md is unstructured
-		// reference too. None of these are reusable lessons (K).
-		e.Tier = "note"
+		// Pre-M3 wiki layout. Most subdirs are I-level:
+		//   wiki/sources/  — synth summaries of raw inbox material
+		//   wiki/concepts/ — definitions, not lessons
+		// One exception: wiki/entities/ holds anchor facts about
+		// concrete things (models, services, people) that the eval
+		// expects to surface when queried directly. Those map to K
+		// to match the post-M3 layout target (knowledge/facts/).
+		if len(parts) >= 2 && parts[1] == "entities" {
+			e.Tier = "knowledge"
+		} else {
+			e.Tier = "note"
+		}
 	case "raw", "sessions", "clips":
 		e.Tier = "inbox"
 	}