Add fragment blueprint + sync shared: micro-frontend infrastructure

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

app.py

@@ -11,6 +11,7 @@ from shared.services.registry import services
 from bp import (
     register_identity_bp,
     register_social_bp,
+    register_fragments,
 )
 
 
@@ -63,6 +64,7 @@ def create_app() -> "Quart":
     # by the shared AP blueprint registered in create_base_app().
     app.register_blueprint(register_identity_bp())
     app.register_blueprint(register_social_bp())
+    app.register_blueprint(register_fragments())
 
     # --- home page ---
     @app.get("/")