feat: add admin UI frontend and complete backend APIs

- Add Vue 3 frontend with Element Plus
- Implement login, dashboard, tenant management
- Add app configuration, logs viewer, stats pages
- Add user management for admins
- Update Drone CI to build and deploy frontend
- Frontend ports: 3001 (test), 4001 (prod)

frontend/vite.config.js

@@ -0,0 +1,25 @@
+import { defineConfig } from 'vite'
+import vue from '@vitejs/plugin-vue'
+import { resolve } from 'path'
+
+export default defineConfig({
+  plugins: [vue()],
+  resolve: {
+    alias: {
+      '@': resolve(__dirname, 'src')
+    }
+  },
+  server: {
+    port: 3001,
+    proxy: {
+      '/api': {
+        target: 'http://localhost:8001',
+        changeOrigin: true
+      }
+    }
+  },
+  build: {
+    outDir: 'dist',
+    sourcemap: false
+  }
+})