Wire federation service stub and update shared submodule

- Register StubFederationService in services/__init__.py
- Add federation to CI sibling list
- Add federation URL to app-config.yaml
- Update shared submodule with federation models/contracts/services

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

services/__init__.py

@@ -24,3 +24,6 @@ def register_domain_services() -> None:
         services.market = SqlMarketService()
     if not services.has("cart"):
         services.cart = SqlCartService()
+    if not services.has("federation"):
+        from shared.services.stubs import StubFederationService
+        services.federation = StubFederationService()