chore: add Docker deployment setup and health check wiring

- Add multi-stage Dockerfile for backend (SDK build → ASP.NET runtime,
  non-root user, /health HEALTHCHECK)
- Add docker-compose.dev.yml orchestrating extrudex-api + control-center-web
- Add deploy.sh convenience script wrapping docker compose up --build
- Wire ASP.NET health checks: AddHealthChecks().AddNpgSql() + MapHealthChecks("/health")
- Add backend .dockerignore (comprehensive pattern list)
- Exclude frontend/dist, frontend/node_modules, frontend/.angular from git

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

backend/.dockerignore

@@ -0,0 +1,27 @@
+# Build artifacts
+bin/
+obj/
+
+# IDE / editor
+.vs/
+.vscode/
+*.user
+*.suo
+.idea/
+
+# Environment & secrets
+appsettings.Development.json
+.env
+.env.*
+
+# Docker
+Dockerfile
+.dockerignore
+
+# OS
+.DS_Store
+Thumbs.db
+
+# Misc
+*.md
+*.log