chore(config): configure CORS and update frontend URL in development settings

Set up CORS policy to allow requests from frontend development server and
update development.yaml with proper frontend origin URL configuration.

Ref: T011 (specs/001-modbus-relay-control)

backend/settings/development.yaml

@@ -1,4 +1,4 @@
-frontend_url: http://localhost:3000
+frontend_url: http://localhost:5173
 debug: true
 
 application:
@@ -6,3 +6,8 @@ application:
   host: 127.0.0.1
   base_url: http://127.0.0.1:3100
   name: "sta-dev"
+
+cors:
+  allowed_origins: ["*"]
+  allow_credentials: false
+  max_age_secs: 3600