Add fragment blueprint + sync shared: micro-frontend infrastructure

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

app.py

@@ -15,6 +15,7 @@ from bp import (
     register_admin,
     register_menu_items,
     register_snippets,
+    register_fragments,
 )
 
 
@@ -73,6 +74,7 @@ def create_app() -> "Quart":
     app.register_blueprint(register_admin("/settings"))
     app.register_blueprint(register_menu_items())
     app.register_blueprint(register_snippets())
+    app.register_blueprint(register_fragments())
 
     # --- KV admin endpoints ---
     @app.get("/settings/kv/<key>")