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>

asset/nginx/rpm.lair.cafe.conf

@@ -10,16 +10,17 @@ server {
 
     root /var/www/rpm;
 
-    autoindex on;
-    autoindex_exact_size off;
-    autoindex_localtime on;
-
     types {
         application/x-rpm rpm;
         application/xml xml;
     }
     default_type application/octet-stream;
 
+    location /assets/ {
+        expires 1y;
+        add_header Cache-Control "public, immutable";
+    }
+
     location ~ \.rpm$ {
         expires 30d;
         add_header Cache-Control "public, immutable";
@@ -30,7 +31,16 @@ server {
         add_header Cache-Control "no-cache, must-revalidate";
     }
 
+    location ~ packages\.json$ {
+        expires 5m;
+        add_header Cache-Control "public, must-revalidate";
+    }
+
     location ~ \.gpg$ {
         default_type text/plain;
     }
+
+    location / {
+        try_files $uri $uri/ /index.html;
+    }
 }