Version 0.2.0

Implemented the admin settings UI (Environments & Detection tab, per-environment tabs, custom field repeater, extension field groups).
Implemented saving of per-environment settings with type-aware sanitization (code snippets stored as-is, relying on administrator capability).
Added environment set management (up to 10; production and staging cannot be removed) and detection method selection.
Implemented automatic front-end output of the standard fields (GTM / GA4). Output is suspended while the environment is undetermined.