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/pages/ComfyUI.tsx

@@ -1,37 +0,0 @@
-import React from 'react';
-
-export default function ComfyUI() {
-  const [isDark, setIsDark] = React.useState(true);
-
-  React.useEffect(() => {
-    const el = document.documentElement;
-    const check = () => setIsDark(el.getAttribute('data-theme') !== 'light');
-    check();
-    const mo = new MutationObserver(check);
-    mo.observe(el, { attributes: true, attributeFilter: ['data-theme'] });
-    return () => mo.disconnect();
-  }, []);
-
-  return (
-    <div
-      style={{
-        width: '100%',
-        height: 'calc(100vh - 56px)',
-        display: 'flex',
-        flexDirection: 'column',
-        background: isDark ? '#1a1a2e' : '#f5f5f5',
-      }}
-    >
-      <iframe
-        src="/comfyui"
-        style={{
-          width: '100%',
-          height: '100%',
-          border: 'none',
-        }}
-        title="ComfyUI"
-        allow="clipboard-read; clipboard-write"
-      />
-    </div>
-  );
-}