Decoupling audit: remove coop_api, fix blog admin calendar imports

- Delete coop_api.py (dead internal API endpoint)
- Replace cross-app calendar imports with shared service calls
- Update shared submodule

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

app.py

@@ -16,7 +16,6 @@ from bp import (
     register_admin,
     register_menu_items,
     register_snippets,
-    register_coop_api,
 )
 
 
@@ -78,9 +77,6 @@ def create_app() -> "Quart":
     app.register_blueprint(register_menu_items())
     app.register_blueprint(register_snippets())
 
-    # Internal API (server-to-server, CSRF-exempt)
-    app.register_blueprint(register_coop_api())
-
     # --- KV admin endpoints ---
     @app.get("/settings/kv/<key>")
     async def kv_get(key: str):