refactor: purge Node.js, Rust is the one true backend

- Moved boosapi-rs/* to repo root
- Deleted all Node.js source (src/server/, src/web/, scripts/)
- Deleted node_modules, package.json, tsconfig, vite.config
- Updated .gitignore and AGENTS.md for Rust-only stack
- Fixed static file path for frontend dist/web/
- Dockerfile stays the same (already Rust-only)
- Kept dist/web/ for Rust static serving

src/web/index.html

@@ -1,27 +0,0 @@
-<!DOCTYPE html>
-<html lang="zh-CN">
-<head>
-  <meta charset="UTF-8" />
-  <meta name="viewport" content="width=device-width, initial-scale=1.0" />
-  <meta name="description" content="BoosAPI - 中转站的中转站，聚合多个 AI API 中转站为统一网关" />
-  <title>BoosAPI</title>
-  <link rel="icon" type="image/png" href="/favicon.png" />
-  <link rel="preconnect" href="https://fonts.googleapis.com" />
-  <link rel="preconnect" href="https://fonts.gstatic.com" crossorigin />
-  <link href="https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700&display=swap" rel="stylesheet" />
-</head>
-<body class="min-h-screen">
-  <script>
-    (function(){
-      var t = localStorage.getItem('theme');
-      if (t === 'dark' || (!t && window.matchMedia('(prefers-color-scheme: dark)').matches)) {
-        document.documentElement.setAttribute('data-theme', 'dark');
-      } else {
-        document.documentElement.setAttribute('data-theme', 'light');
-      }
-    })();
-  </script>
-  <div id="root"></div>
-  <script type="module" src="./main.tsx"></script>
-</body>
-</html>