feat: Introduce dedicated settings page with API URL configuration and data management hooks, and update Dockerfile for runtime env injection.

k-notes-frontend/public/env-config.js

@@ -0,0 +1,5 @@
+// Default environment configuration for development
+// This file is replaced at Docker container startup with runtime values
+window.env = {
+    // API_URL will be injected by Docker, or can be overridden via localStorage
+};