V198: withholds the secret-named setting values the settings history has already recorded.

The settings history writes a permanent setting.changed activity entry for every settings write, with the value before and after — except for secrets, whose values it withholds. After V194 it recognised a secret by the restricted-key list and by an integration row's module. That list only names the keys core knows: a module's own …_api_key, …_webhook_secret or …_token written through the ordinary writers was withheld from the change broadcast (PhoenixKit.Settings.Events.secret_key?/2, which also reads the key's NAME) and then stored in the history in plain text — in an entry that is never pruned and that the admin Activity page shows to anyone who can open it.

The writer now applies the same name test. This migration withholds what it already wrote, exactly as a restricted setting is recorded: from and to become null and restricted true. The rest of each entry — who, when, which key — stays, so the history still says that the setting changed.

An entry is withheld when its key, lower-cased, contains one of the fragments the writer tests for: secret, password, passwd, token, private_key, api_key, apikey, credential, webhook. The list is frozen here as it stood when this version shipped; a fragment added to the writer later needs a version of its own to reach entries already written.

Re-runnable: an entry already restricted is left alone.

down/1

Moves the version marker back and nothing else. The withheld values are gone on purpose; restoring them is the defect this version removes.