docs: add Coolify and AWS ECS deployment guides

- Rewrite deployment-guide.md as a concise overview linking to platform-specific guides
- Create deploy-coolify.md: detailed step-by-step based on actual production deploy
- Create deploy-aws-ecs.md: realistic AWS guide with Docker socket constraints
- Update self-hosting.md: fix PEM format docs, add VITE_GITHUB_APP_SLUG, OAuth token notes
- Update mkdocs.yml nav: add Deployment section, move self-hosting and skills to Guides

Author: mariuspruvot