Remove blog auth blueprint — login/account now in federation

All auth routes (login, magic link, account, newsletters,
widget pages, logout) are handled by the federation app.

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

app.py

@@ -11,7 +11,6 @@ from shared.config import config
 from shared.models import KV
 
 from bp import (
-    register_auth_bp,
     register_blog_bp,
     register_admin,
     register_menu_items,
@@ -63,8 +62,6 @@ def create_app() -> "Quart":
     ])
 
     # --- blueprints ---
-    app.register_blueprint(register_auth_bp())
-
     app.register_blueprint(
         register_blog_bp(
             url_prefix=config()["blog_root"],