Add Docker and Gitea workflow configurations for Talks slides deployment

- Introduced .dockerignore to exclude unnecessary files from Docker builds.
- Added build-and-push.yaml workflow for automated image building and Helm chart deployment on changes to specific paths.
- Created Dockerfile for building a static site with Nginx, including configuration for serving slides.
- Established Helm chart structure in talks-slides-dist for managing deployment configurations and resources.
- Removed outdated GitHub Actions workflows to streamline CI/CD processes.

.dockerignore

@@ -0,0 +1,14 @@
+# Contexte Docker = racine du dépôt (voir server/Dockerfile)
+node_modules
+dist-portal
+dist-*
+artifacts
+.git
+.github
+e2e
+playwright-report
+test-results
+blob-report
+playwright/.cache
+.cursor
+*.log