Add server security configs and setup script

- Nginx configs with security headers (X-Frame-Options, CSP, etc.)
- fail2ban jails for nginx (botsearch, bad-request, forbidden)
- Kernel hardening via sysctl (rp_filter, no redirects, log martians)
- SSH hardening (no root, max 3 attempts, no X11)
- UFW rules export
- Idempotent setup.sh to restore all configs on fresh install
- Flask bound to 127.0.0.1 (nginx-only access)

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

server/nginx-llms3.conf

@@ -0,0 +1,26 @@
+server {
+    listen 80 default_server;
+    server_name llms3.com www.llms3.com 192.168.1.176;
+
+    # Security headers
+    add_header X-Frame-Options "SAMEORIGIN" always;
+    add_header X-Content-Type-Options "nosniff" always;
+    add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+    add_header Permissions-Policy "camera=(), microphone=(), geolocation=()" always;
+    add_header X-XSS-Protection "1; mode=block" always;
+
+    location ^~ /.well-known/ {
+        root /var/www/html/llms3;
+        default_type "text/plain";
+        try_files $uri =404;
+    }
+
+    location / {
+        proxy_pass http://127.0.0.1:5000;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        proxy_set_header X-Real-IP $remote_addr;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+    }
+}