Remove auth blueprint, federation is now an OAuth client

Auth server responsibilities moved to account app.
Federation uses the shared OAuth client blueprint via factory.

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

app.py

@@ -12,7 +12,6 @@ from bp import (
     register_wellknown_bp,
     register_actors_bp,
     register_identity_bp,
-    register_auth_bp,
     register_social_bp,
 )
 
@@ -65,7 +64,6 @@ def create_app() -> "Quart":
     app.register_blueprint(register_wellknown_bp())
     app.register_blueprint(register_actors_bp())
     app.register_blueprint(register_identity_bp())
-    app.register_blueprint(register_auth_bp())
     app.register_blueprint(register_social_bp())
 
     # --- home page ---