postiz-app: Channel tokens and organization API key exposed in API responses

Several Postiz endpoints return the complete database row of the record they operate on instead of only the fields the client needs. Two of them include secrets the caller is not meant to receive.

The public API's channel delete returns the deleted integration row, including the channel's platform access token and refresh token. A third-party OAuth app permitted to delete a channel therefore receives that channel's social platform credentials and can use them against the connected account directly, outside Postiz.

GET /user/organizations returns each organization row, including its API key, to every member of the organization. The API key is intended for admins only, so a member with a lower role can obtain it and call the public API on behalf of the organization.

Both endpoints require a valid session, API key or OAuth token and are scoped to the caller's own organization. There is no anonymous access and no cross-tenant exposure.