Add glue layer: replace /internal/menu-items API with direct DB query

- Context processor: get_navigation_tree() replaces api_get("coop", "/internal/menu-items")
- Add glue submodule

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

.gitmodules

@@ -2,3 +2,6 @@
 	path = shared
 	url = https://git.rose-ash.com/coop/shared.git
 	branch = decoupling
+[submodule "glue"]
+	path = glue
+	url = /root/rose-ash/glue