Explicit masterfeats/feats removal

internal/topdata/MASTERFEATS_CONTRACT.md

@@ -44,7 +44,9 @@ Canonical shape:
 
 Rules:
 
-- `output` must be exactly `masterfeats.2da`
+- `output` may be omitted; native dataset discovery deterministically derives
+  `masterfeats.2da` from `topdata/data/masterfeats/base.json`
+- if `output` is present, it must be exactly `masterfeats.2da`
 - `columns` must include `LABEL`, `STRREF`, and `DESCRIPTION`
 - every canonical row must have a non-empty `key`
 - row keys must start with `masterfeats:`