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>

.gitea/workflows/ci.yml

@@ -40,11 +40,11 @@ jobs:
             git reset --hard origin/${{ github.ref_name }}
             git submodule update --init --recursive
             # Clean ALL sibling dirs (including stale self-copies from previous runs)
-            for sibling in blog market cart events; do
+            for sibling in blog market cart events federation; do
               rm -rf \$sibling
             done
             # Copy non-self sibling models for cross-domain imports
-            for sibling in blog market cart events; do
+            for sibling in blog market cart events federation; do
               [ \"\$sibling\" = \"${{ env.IMAGE }}\" ] && continue
               repo=/root/rose-ash/\$sibling
               if [ -d \$repo/.git ]; then