docs: start hub-core absorption foundation

docs/specs/runtime-absorption-plan.md

@@ -47,9 +47,10 @@ Core Hub models and migrations are not imported. Deployment remains owned by
 `rapp-core-hub` during dual-run, with final package naming/ownership recorded
 before this repository is archived.
 
-## Entry gates
+## Public route movement gates
 
-Absorption implementation does not begin until all of these are evidenced:
+S0 may build the missing foundation, but no public route group leaves Core Hub
+until all of these are evidenced:
 
 - the completed `HUB-WP-0004-T01`–`T05` work is committed and pushed;
 - a hub-core wheel and OCI image identify the same revision and version;
@@ -178,7 +179,7 @@ keeps public authority on Core Hub.
 
 ## Next executable work
 
-After hub-core publishes its completed T01–T06 revision, start S0. The
-first implementation commit should add the durable PostgreSQL boundary and
-legacy auth/health compatibility in hub-core, plus a candidate deployment mode
-in `rapp-core-hub`. It must not change public DNS or ingress.
+Hub-core published its completed T01–T06 work as revision `7e1ec03`; S0 is now
+active. Its first implementation commit adds the durable PostgreSQL boundary
+and legacy auth/health compatibility in hub-core, followed by a candidate
+deployment mode in `rapp-core-hub`. It must not change public DNS or ingress.