Add canonical party domain and players projection

internal/config/party_legacy.go

@@ -0,0 +1,8 @@
+package config
+
+// classifyLegacyPartyDocument is the bounded compatibility path for an
+// unversioned party source. It intentionally retains no parsed roster data and
+// must be removed once legacy campaign inputs are no longer supported.
+func classifyLegacyPartyDocument() *PartyDocument {
+	return &PartyDocument{Mode: PartyModeLegacy}
+}