feat: add initial multi-environment CI/CD pipeline POC

Adds all required files for the proof of concept:
- Gitea Actions CI/CD workflows for QA, staging, and production environments
- Docker build configuration with healthcheck and runtime environment injection
- Nginx server config with security headers and health endpoint
- Sample static frontend application displaying environment metrics
- Comprehensive README documentation with architecture, setup, and usage instructions

nginx.conf

@@ -0,0 +1,58 @@
+worker_processes auto;
+pid /var/run/nginx.pid;
+
+events {
+  worker_connections 1024;
+  multi_accept on;
+}
+
+http {
+  include /etc/nginx/mime.types;
+  default_type application/octet-stream;
+
+  server_tokens off;
+
+  gzip on;
+  gzip_comp_level 6;
+  gzip_min_length 256;
+  gzip_proxied any;
+  gzip_types text/plain text/css application/json application/javascript text/xml application/xml application/xml+rss text/javascript image/svg+xml;
+
+  add_header X-Frame-Options "DENY" always;
+  add_header X-Content-Type-Options "nosniff" always;
+  add_header X-XSS-Protection "1; mode=block" always;
+  add_header Referrer-Policy "strict-origin-when-cross-origin" always;
+  add_header Permissions-Policy "camera=(), microphone=(), geolocation=()" always;
+
+  server {
+    listen 80;
+    root /usr/share/nginx/html;
+    index index.html;
+
+    location = /health {
+      default_type application/json;
+      add_header Cache-Control "no-store, no-cache, must-revalidate";
+      return 200 '{"status":"ok","env":"${APP_ENV:-development}","version":"${APP_VERSION:-0.0.0}","timestamp":"$time_iso8601"}';
+    }
+
+    location / {
+      try_files $uri $uri/ /index.html;
+      add_header Cache-Control "no-cache, must-revalidate";
+    }
+
+    location ~* \.(js|css|png|jpg|jpeg|gif|ico|svg|woff|woff2|ttf|eot)$ {
+      expires 30d;
+      add_header Cache-Control "public, immutable";
+    }
+
+    location = /favicon.ico {
+      log_not_found off;
+      access_log off;
+    }
+
+    location = /robots.txt {
+      log_not_found off;
+      access_log off;
+    }
+  }
+}