YAML Formatting VSCode Settings

Different people may have different default YAML formatters configured in their user settings. These may even fight each other in multi-author PRs and similar. We should decide on one and put it in the repo settings.

## Acceptance Critera
- `.vscode/settings.json` includes a default YAML formatter
- Recommended extension settings includes the extension used if applicable

Start by inspecting .vscode/settings.json and the repository's recommended extension settings. Decide on a single YAML formatter and record its default setting and extension recommendation there. Done means the acceptance criteria are satisfied and the repository consistently identifies one formatter.

Rédigé par le modèle d'indexation à partir du texte de l'issue.