feat: align portal center panel with side cards + redesign login page

- Portal: wrap .panel-head in matching card (border, radius, shadow) with
  cyan->purple left accent bar; h2 28px -> 20px; description right-aligned
  with vertical divider; top edge now aligns with side-menu & links-panel
- Login: switch from absolute-positioned icons to el-input prefix slot;
  layout brand row (logo + title + uppercase subtitle); add form-title
  section with gradient bar; consistent cyan focus; gradient button;
  dashed top divider for back-link; card width 420 -> 460
- Add .gitignore (node_modules, dist, __pycache__, .env, etc.)

frontend/vite.config.js

@@ -0,0 +1,18 @@
+import { defineConfig } from 'vite'
+import vue from '@vitejs/plugin-vue'
+
+export default defineConfig({
+  plugins: [vue()],
+  server: {
+    host: '0.0.0.0',
+    port: 3001,
+    allowedHosts: true,
+    proxy: {
+      '/api': { target: 'http://127.0.0.1:8090', changeOrigin: true }
+    }
+  },
+  build: {
+    outDir: 'dist',
+    chunkSizeWarningLimit: 1500
+  }
+})