feat(spa): add USE_SPA_UI cutover flag with legacy fallback

partyhub/settings.py

@@ -99,6 +99,14 @@ STATIC_ROOT = BASE_DIR / 'staticfiles'
 
 DEFAULT_AUTO_FIELD = 'django.db.models.BigAutoField'
 
+
+USE_SPA_UI_RAW = env('USE_SPA_UI')
+if USE_SPA_UI_RAW is None:
+    # Backward-compatible fallback while cutover is rolling out.
+    USE_SPA_UI_RAW = env('WPP_SPA_ENABLED', 'false')
+USE_SPA_UI = USE_SPA_UI_RAW.lower() == 'true'
+WPP_SPA_ASSET_BASE = env('WPP_SPA_ASSET_BASE', '/static/frontend/angular/browser').rstrip('/')
+
 CHANNEL_REDIS_HOST = env('CHANNEL_REDIS_HOST', '127.0.0.1')
 CHANNEL_REDIS_PORT = int(env('CHANNEL_REDIS_PORT', '6379'))
 CHANNEL_LAYERS = {