Chore: organize files, update devcontainer

[thekaveman]

Closes #123

This PR moves all the website source files under the /src directory for better organization.

Also cleans up and normalizes the devcontainer setup with our other repositories:

• settings.json for VS Code settings
• .prettierrc for Prettier config
• fix customization syntax in devcontainer.json
• run the devcontainer as a non-root user

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[thekaveman]

Rebased to resolve conflicts