ci: add Gitea Actions CI/CD with Portainer deployment

Add complete CI/CD pipeline:
- Gitea Actions workflow (build + deploy)
- Multi-stage Dockerfile (Node build + nginx serve)
- nginx config with SPA routing and cache headers
- docker-compose.yml for local testing
- .dockerignore to optimize build

Pipeline flow:
1. Build job: npm ci + npm build + upload artifact
2. Deploy job (main only): Docker build + push to registry + Portainer webhook

Requires Gitea secrets:
- DOCKER_USERNAME
- DOCKER_PASSWORD
- PORTAINER_WEBHOOK_URL

docker-compose.yml

@@ -0,0 +1,17 @@
+version: '3.8'
+
+services:
+  portfolio:
+    build: .
+    container_name: davidaragon-portfolio
+    ports:
+      - "8080:80"
+    restart: unless-stopped
+    environment:
+      - NODE_ENV=production
+    healthcheck:
+      test: ["CMD", "wget", "--no-verbose", "--tries=1", "--spider", "http://localhost/"]
+      interval: 30s
+      timeout: 3s
+      retries: 3
+      start_period: 5s