add session-based connection management and React dashboard

Backend: adds JDBC session support, login/status/logout endpoints, and
new DTOs (AuthResponse, ConnectionStatusResponse, LoginResult). Frontend
replaces the Vite boilerplate with a Dashboard, ServiceCard, and
ConnectModal backed by a typed API client.

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

frontend/vite.config.ts

@@ -1,12 +1,21 @@
-import { defineConfig } from 'vite'
+import { defineConfig, loadEnv } from 'vite'
 import react from '@vitejs/plugin-react'
 
-// https://vite.dev/config/
-export default defineConfig({
-  plugins: [react()],
-  server: {
-    host: '0.0.0.0',
-    port: 5173,
-    allowedHosts: ['5173.code-server.kasuns.website'],
-  },
+export default defineConfig(({ mode }) => {
+  const env = loadEnv(mode, process.cwd(), '');
+
+  return {
+    plugins: [react()],
+    server: {
+      host: '0.0.0.0',
+      port: 5173,
+      allowedHosts: env.FRONTEND_URL ? [env.FRONTEND_URL] : [],
+      proxy: {
+        '/api': {
+          target: 'http://localhost:8080',
+          changeOrigin: true,
+        },
+      },
+    },
+  }
 })