feat(Button): add support for inverse filled color (#1872)

## 📝 Changes

- Add support for `inverse` color on `filled` variant

<img width="274" height="121" alt="image"
src="https://github.com/user-attachments/assets/73d4c47e-4163-4563-bd87-89328f8f21e3"
/>

## ✅ Checklist

Easy UI has certain UX standards that must be met. In general,
non-trivial changes should meet the following criteria:

- [-] Visuals match Design Specs in Figma (within our current color
system)
- [x] Stories accompany any component changes
- [x] Code is in accordance with our style guide
- [x] Design tokens are utilized
- [x] Unit tests accompany any component changes
- [x] TSDoc is written for any API surface area
- [x] Specs are up-to-date
- [x] Console is free from warnings
- [x] No accessibility violations are reported
- [x] Cross-browser check is performed (Chrome, Safari, Firefox)
- [x] Changeset is added

~Strikethrough~ any items that are not applicable to this pull request.

Author: stephenjwatkins

.changeset/four-guests-return.md

@@ -0,0 +1,5 @@
+---
+"@easypost/easy-ui": minor
+---
+
+feat(Button): add support for inverse filled color

easy-ui-react/src/Button/_mixins.scss

@@ -187,6 +187,8 @@
 
 // prettier-ignore
 @mixin colorInverse {
+  @include component-token("button", "filled.font.color", design-token("color.primary.800"));
+  @include component-token("button", "filled.active.font.color", design-token("color.primary.800"));
   @include component-token("button", "resting.color", design-token("color.neutral.000"));
   @include component-token("button", "hover.focus.color", design-token("color.neutral.100"));
   @include component-token("button", "active.color", design-token("color.neutral.200"));

easy-ui-react/src/Button/utilities.ts

@@ -8,6 +8,7 @@ export const FILLED_BUTTON_COLORS = [
   "success",
   "warning",
   "neutral",
+  "inverse",
 ];
 
 export const OUTLINED_BUTTON_COLORS = [

easy-ui-react/src/utilities/storybook.tsx

@@ -69,7 +69,7 @@ export function getFilledButtonsColorMapping() {
       table: {
         type: {
           summary:
-            '"primary" | "secondary" | "success" | "warning" | "neutral"',
+            '"primary" | "secondary" | "success" | "warning" | "neutral" | "inverse"',
         },
         defaultValue: { summary: "primary" },
       },