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/package.json

@@ -0,0 +1,25 @@
+{
+  "name": "ui",
+  "private": true,
+  "version": "0.0.0",
+  "type": "module",
+  "scripts": {
+    "dev": "vite",
+    "build": "tsc && vite build",
+    "preview": "vite preview"
+  },
+  "devDependencies": {
+    "@types/react": "^19.2.14",
+    "@types/react-dom": "^19.2.3",
+    "@vitejs/plugin-react-swc": "^4.3.0",
+    "typescript": "~6.0.2",
+    "vite": "^8.0.10"
+  },
+  "dependencies": {
+    "bootstrap": "^5.3.8",
+    "react": "^19.2.5",
+    "react-bootstrap": "^2.10.10",
+    "react-dom": "^19.2.5",
+    "react-router": "^7.14.2"
+  }
+}