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

docker-entrypoint.sh

@@ -0,0 +1,24 @@
+#!/bin/sh
+set -euo pipefail
+
+APP_ENV="${APP_ENV:-development}"
+APP_VERSION="${APP_VERSION:-0.0.0}"
+BUILD_DATE="${BUILD_DATE:-}"
+GIT_COMMIT="${GIT_COMMIT:-}"
+GIT_BRANCH="${GIT_BRANCH:-}"
+DEPLOY_TIME="${DEPLOY_TIME:-}"
+BUILD_NUMBER="${BUILD_NUMBER:-}"
+
+cat > /usr/share/nginx/html/env-config.js << EOF
+window.__ENV__ = {
+  APP_ENV: "${APP_ENV}",
+  APP_VERSION: "${APP_VERSION}",
+  BUILD_DATE: "${BUILD_DATE}",
+  GIT_COMMIT: "${GIT_COMMIT}",
+  GIT_BRANCH: "${GIT_BRANCH}",
+  DEPLOY_TIME: "${DEPLOY_TIME}",
+  BUILD_NUMBER: "${BUILD_NUMBER}"
+};
+EOF
+
+exec "$@"