fix(store/pg): error-propagate parseUUID in kg dedup insert paths

insertDedupCandidate and ScanDuplicates both swallowed uuid.Parse
errors before feeding entity IDs to the INSERT. Currently safe
because all inputs originate from DB SELECT rows or caller-validated
UUIDs, but aligning with parseUUID keeps write-path policy uniform:
bad UUID → clean Go error + skip, not silent uuid.Nil write.

internal/store/pg/knowledge_graph_dedup.go

@@ -148,10 +148,16 @@ func (s *PGKnowledgeGraphStore) insertDedupCandidate(ctx context.Context, agentI
 	if entityAID > entityBID {
 		entityAID, entityBID = entityBID, entityAID
 	}
-	aID, _ := uuid.Parse(entityAID)
-	bID, _ := uuid.Parse(entityBID)
+	aID, err := parseUUID(entityAID)
+	if err != nil {
+		return fmt.Errorf("insert dedup candidate: entity_a_id: %w", err)
+	}
+	bID, err := parseUUID(entityBID)
+	if err != nil {
+		return fmt.Errorf("insert dedup candidate: entity_b_id: %w", err)
+	}
 	tid := tenantIDForInsert(ctx)
-	_, err := s.db.ExecContext(ctx, `
+	_, err = s.db.ExecContext(ctx, `
 		INSERT INTO kg_dedup_candidates (id, tenant_id, agent_id, user_id, entity_a_id, entity_b_id, similarity, created_at)
 		VALUES ($1, $2, $3, $4, $5, $6, $7, $8)
 		ON CONFLICT (entity_a_id, entity_b_id) DO NOTHING`,
@@ -229,8 +235,16 @@ func (s *PGKnowledgeGraphStore) ScanDuplicates(ctx context.Context, agentID, use
 		if aID > bID {
 			aID, bID = bID, aID
 		}
-		aUUID, _ := uuid.Parse(aID)
-		bUUID, _ := uuid.Parse(bID)
+		aUUID, err := parseUUID(aID)
+		if err != nil {
+			slog.Warn("kg.scan_duplicates: invalid entity_a UUID from DB row", "id", aID, "error", err)
+			continue
+		}
+		bUUID, err := parseUUID(bID)
+		if err != nil {
+			slog.Warn("kg.scan_duplicates: invalid entity_b UUID from DB row", "id", bID, "error", err)
+			continue
+		}
 		if _, err := s.db.ExecContext(ctx, `
 			INSERT INTO kg_dedup_candidates (id, tenant_id, agent_id, user_id, entity_a_id, entity_b_id, similarity, created_at)
 			VALUES ($1, $2, $3, $4, $5, $6, $7, $8)