relations: Phase 1 schema + direct relations (rel facts, relate/unrelate, children/parents/related) + 22 tests

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/relations/conformance.conf

@@ -0,0 +1,23 @@
+# relations conformance config — sourced by lib/guest/conformance.sh.
+
+LANG_NAME=relations
+MODE=dict
+
+PRELOADS=(
+  lib/datalog/tokenizer.sx
+  lib/datalog/parser.sx
+  lib/datalog/unify.sx
+  lib/datalog/db.sx
+  lib/datalog/builtins.sx
+  lib/datalog/aggregates.sx
+  lib/datalog/strata.sx
+  lib/datalog/eval.sx
+  lib/datalog/api.sx
+  lib/datalog/magic.sx
+  lib/relations/schema.sx
+  lib/relations/api.sx
+)
+
+SUITES=(
+  "direct:lib/relations/tests/direct.sx:(relations-direct-tests-run!)"
+)