host: Phase 3 — relations READ cut-over (get-children/get-parents), 121/121

Migrate the two internal relations read queries onto lib/relations: GET
/internal/data/get-children + /get-parents dispatch to relations/children
and relations/parents. Bridge the Quart (type,id) node key to a graph atom
symbol "type:id" with relation-type as the edge kind; optional child/parent
-type params filter by "type:" prefix. Golden tests pin each endpoint to
subsystem-call + envelope. Ledger entries flipped to :migrated (off-Quart
coverage 27% -> 45%).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

lib/host/conformance.sh

@@ -46,6 +46,12 @@ MODULES=(
   "lib/acl/audit.sx"
   "lib/acl/federation.sx"
   "lib/acl/api.sx"
+  "lib/relations/schema.sx"
+  "lib/relations/engine.sx"
+  "lib/relations/api.sx"
+  "lib/relations/explain.sx"
+  "lib/relations/federation.sx"
+  "lib/relations/tree.sx"
   "lib/feed/normalize.sx"
   "lib/feed/stream.sx"
   "lib/feed/api.sx"
@@ -59,6 +65,7 @@ MODULES=(
   "lib/host/sxtp.sx"
   "lib/host/router.sx"
   "lib/host/feed.sx"
+  "lib/host/relations.sx"
   "lib/host/ledger.sx"
 )
 
@@ -69,6 +76,7 @@ SUITES=(
   "sxtp        host-sx-tests-run!  lib/host/tests/sxtp.sx"
   "router      host-rt-tests-run!  lib/host/tests/router.sx"
   "feed        host-fd-tests-run!  lib/host/tests/feed.sx"
+  "relations   host-rl-tests-run!  lib/host/tests/relations.sx"
   "ledger      host-lg-tests-run!  lib/host/tests/ledger.sx"
 )