feat: add dedicated color tokens for voice call widget (#14745)

# Pull Request Template

## Description

This PR introduces dedicated color tokens for the floating voice call
widget instead of reusing generic design tokens. This allows the widget
to maintain a distinct dark-card appearance across both light and dark
themes.

Adds the following tokens and applies them to `CallCard`:

* `--call-widget`
* `--call-widget-border`
* `--call-widget-text`
* `--call-widget-sub-text`

Fixes
https://linear.app/chatwoot/issue/CW-7353/call-notification-window-theme-update-design

## Type of change

- [x] New feature (non-breaking change which adds functionality)

## How Has This Been Tested?

### Screenshots

**Light mode**
<img width="1466" height="815" alt="Screenshot 2026-06-16 at 3 47 32 PM"
src="https://github.com/user-attachments/assets/732164b1-5488-4cc1-8c71-01245d906842"
/>


**Dark mode**
<img width="1466" height="815" alt="Screenshot 2026-06-16 at 3 46 54 PM"
src="https://github.com/user-attachments/assets/536ab632-4c7c-486b-8fc4-a061ee40b22a"
/>



## Checklist:

- [x] My code follows the style guidelines of this project
- [x] I have performed a self-review of my code
- [x] I have commented on my code, particularly in hard-to-understand
areas
- [ ] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [x] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged and published in downstream
modules

app/javascript/dashboard/assets/scss/_next-colors.scss

@@ -145,6 +145,12 @@
     --black-alpha-2: 0, 0, 0, 0.04;
     --border-blue: 39, 129, 246, 0.5;
     --white-alpha: 255, 255, 255, 0.8;
+
+    // Voice call widget - light mode
+    --call-widget: 33, 34, 38, 0.95;
+    --call-widget-border: 255, 255, 255, 0.1;
+    --call-widget-text: 237, 238, 240, 1;
+    --call-widget-sub-text: 173, 177, 184, 1;
   }
 
   .dark {
@@ -291,6 +297,12 @@
     --border-blue: 39, 129, 246, 0.5;
     --border-container: 255, 255, 255, 0;
     --white-alpha: 255, 255, 255, 0.1;
+
+    // Voice call widget - dark mode
+    --call-widget: 50, 53, 61, 1;
+    --call-widget-border: 255, 255, 255, 0.07;
+    --call-widget-text: 237, 238, 240, 1;
+    --call-widget-sub-text: 173, 177, 184, 1;
   }
 }
 // NEXT COLORS END