Create connection plugin

Mints a single-use linking token and answers with a presigned download URL for a personalized Modular Connector plugin package: installing it on the website registers the connection with no credentials to enter. The token value itself never travels in the response. **Body** (JSON): - `team` (integer, required) - the team the new website joins once the plugin registers it. - `preset_uptime`, `preset_malware_scan`, `preset_broken_link`, `preset_backup` (integer, nullable) - ids of global configurations to assign the website to as soon as it connects. Any left null is skipped. - `expires_at` (string, nullable, date) - when the linking token itself expires. Defaults to 24 hours from now; sending a later date is capped at 7 days ahead. Answers **200** (not a created resource, so no `Location`) with `meta.download_url` (the presigned plugin ZIP download, itself time-limited) and `meta.expires_at` (the linking token's own expiry). Requires a full-access token (read-only tokens answer 403). A team or preset id that does not belong to your organization answers 404; other validation failures answer 422 with a JSON:API `errors` document.