Notification email footer shows raw notification type key

### Current Behavior

The notification email footer shows the raw notification type key instead of a readable name. For example a mention email reads:

> This email was sent to user@example.com because you are subscribed to "postMentioned" notifications on My Forum.

Any notification type does this, including ones from extensions (e.g. "linkrobinsSupportNewReply").

### Expected Behavior

The footer should show a human readable notification name, like the wording used on the notification settings screen, not the internal type key.

### Steps to Reproduce

1. Receive any notification email (for example a post mention).
2. Read the footer line "...you are subscribed to {type} notifications...".

### Cause

`NotificationMailer` passes the raw type into the footer text:

```php
$type = $blueprint::getType();
```

That value is interpolated directly into `core.email.notification.footer.main_text` as `{type}`, so the machine key is shown verbatim.

Start in NotificationMailer at the code that assigns the blueprint type, then read the core.email.notification.footer.main_text translation that interpolates {type}. Compare the notification settings screen's wording for the same notification, including extension types. Done means notification email footers show a human-readable notification name instead of the raw type key.

Written by the indexing model from the issue text.