Scaffold .vscode/extensions.json

`.vscode/extensions.json` can contain recommendations for extensions

https://docs.runme.dev/configuration/extensions-json/

Would be nice if Nuxt Ignis have a default one

Start with the issue's linked Runme documentation on .vscode/extensions.json and inspect the repository's existing .vscode setup. Add the default extensions.json scaffold requested for Nuxt Ignis, then verify that the file is valid JSON and that the recommended extensions match the project's intended development setup.

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