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/package.json

@@ -0,0 +1,22 @@
+{
+  "name": "ops-portal-frontend",
+  "version": "1.0.0",
+  "private": true,
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "vite build",
+    "preview": "vite preview"
+  },
+  "dependencies": {
+    "axios": "^1.7.9",
+    "element-plus": "^2.9.3",
+    "@element-plus/icons-vue": "^2.3.1",
+    "vue": "^3.5.13",
+    "vue-router": "^4.5.0"
+  },
+  "devDependencies": {
+    "@vitejs/plugin-vue": "^5.2.1",
+    "vite": "^6.0.7"
+  }
+}