feat: add React UI for rpm.lair.cafe

- Vite + React + SWC + TypeScript SPA with react-router and
  react-bootstrap
- Dark/light/system theme with Bootstrap 5.3 data-bs-theme
- Home page with repo setup instructions and copyable code blocks
- Package list and detail pages driven by packages.json
- Python script to generate packages.json from repodata XML
- Nginx config updated for SPA fallback, asset caching, removed
  autoindex
- New deploy-ui workflow triggered on ui/ or nginx config changes,
  requires runners with nvm label
- packages.json generation added to publish job after createrepo_c
- Runner setup docs for nvm and sequoia-sq added to readme

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

ui/vite.config.ts

@@ -0,0 +1,7 @@
+import { defineConfig } from "vite";
+import react from "@vitejs/plugin-react-swc";
+
+export default defineConfig({
+  plugins: [react()],
+  base: "/",
+});