refactor: move personal site to sites/nrd.sh/

Reorganize for monorepo structure:
- Move content/, templates/, static/, site.toml → sites/nrd.sh/
- Frees root for sukr docs site
- Build with: sukr -c sites/nrd.sh/site.toml

sites/nrd.sh/static/_headers

@@ -0,0 +1,25 @@
+# Netlify headers for nrd.sh
+
+# Default headers for all paths
+/*
+  X-Frame-Options: DENY
+  X-Content-Type-Options: nosniff
+  Referrer-Policy: strict-origin-when-cross-origin
+
+# Cache static assets aggressively
+/*.css
+  Cache-Control: public, max-age=31536000, immutable
+
+/*.png
+  Cache-Control: public, max-age=31536000, immutable
+
+/*.gif
+  Cache-Control: public, max-age=31536000, immutable
+
+# HTML pages: short cache, revalidate
+/*.html
+  Cache-Control: public, max-age=3600, must-revalidate
+
+# Feed: moderate cache
+/feed.xml
+  Cache-Control: public, max-age=3600