Add missing semantic tokens for critical & accent buttons

We're missing:

1. A token for critical/pressed buttons
2. Accent button tokens

However when I went to add I noticed inconsistencies with how we've defined tokens:

You can see we have:

```
bg/action/primary/rest
bg/action/primary/hovered
bg/action/primary/pressed
bg/action/secondary/rest
bg/action/secondary/hovered
bg/action/secondary/pressed

bg/critical/primary
bg/critical/hovered
```

when I think instead we should have:

```
bg/action/primary/rest
bg/action/primary/hovered
bg/action/primary/pressed
bg/action/secondary/rest
bg/action/secondary/hovered
bg/action/secondary/pressed
bg/action/critical/rest
bg/action/critical/hovered
bg/action/critical/pressed
bg/action/accent/rest
bg/action/accent/hovered
bg/action/accent/pressed
```

Open questions:

1. Does anyone disagree with unifying the action tokens as above?
2. Should I deprecate the misplaced `bg/critical` tokens in Token Studio? If so, will that introduce any breaking changes?

Review the existing semantic token definitions and the Token Studio setup referenced in the issue, starting with the current bg/action and bg/critical token names. Determine whether the proposed critical and accent states should be unified and whether deprecating the misplaced tokens would break existing consumers. Done means the naming decision, token additions, and deprecation impact are documented and agreed.

Written by the indexing model from the issue text.