feat: node info, build info and acrylic web theme

Squash of recent dev work: return_session login, backend switcher, line
detail timeline, overview strips, node platform/country/ISP info with flags
and icons, build info (version, tag, time) behind site.show_build, and the
acrylic display theme.

web/admin/vite.config.ts

@@ -1,18 +1,22 @@
 import react from '@vitejs/plugin-react'
 import { fileURLToPath } from 'node:url'
 import { defineConfig, loadEnv } from 'vite'
+import { buildDefines } from '../build-info.mjs'
 
 // 开发时把 /api 转发给后端，地址取自环境变量 BACKEND_URL，或 web/.env.local 里的 BACKEND_URL=（见 web/.env.example）：
 //   BACKEND_URL=https://mo.oeo.one npm run dev:display
 export default defineConfig(({ mode }) => {
   const env = loadEnv(mode, fileURLToPath(new URL('..', import.meta.url)), '')
-  const backend = (process.env.BACKEND_URL ?? env.BACKEND_URL ?? 'http://localhost:5000').replace(/\/+$/, '')
+  const backend = (process.env.BACKEND_URL ?? env.BACKEND_URL ?? 'http://localhost:29181').replace(/\/+$/, '')
   return {
     base: '/admin/',
+    define: buildDefines(mode === 'development'),
     plugins: [react()],
     resolve: { alias: { '@shared': fileURLToPath(new URL('../shared', import.meta.url)) } },
     server: {
-      port: 5174,
+      // 5174 常被 Docker Desktop 占用，管理端用 5175；端口被占时直接报错，不悄悄换到别的端口
+      port: 5175,
+      strictPort: true,
       fs: { allow: ['..'] },
       proxy: {
         '/api': { target: backend, changeOrigin: true, secure: true, cookieDomainRewrite: '' },