fix(frontend): color of copy icon for code blocks (#2993)

# Description

Please include a summary of the changes and the related issue. Please
also include relevant motivation and context.

## Checklist before requesting a review

Please delete options that are not relevant.

- [ ] My code follows the style guidelines of this project
- [ ] I have performed a self-review of my code
- [ ] I have commented hard-to-understand areas
- [ ] I have ideally added tests that prove my fix is effective or that
my feature works
- [ ] New and existing unit tests pass locally with my changes
- [ ] Any dependent changes have been merged

## Screenshots (if appropriate):

frontend/app/chat/[chatId]/components/ChatDialogueArea/components/ChatDialogue/components/ChatItem/QADisplay/components/MessageRow/components/MessageContent/MessageContent.tsx

@@ -104,7 +104,7 @@ export const MessageContent = ({
                       <Icon
                         name="copy"
                         size="small"
-                        color="black"
+                        color="static-white"
                         handleHover={true}
                       />
                     </div>

frontend/lib/components/ui/Icon/Icon.module.scss

@@ -67,6 +67,14 @@
   color: var(--icon-0);
 }
 
+.static-white {
+  color: var(--white);
+
+  &:hover {
+    color: var(--primary-0);
+  }
+}
+
 .dangerous {
   color: var(--dangerous);
 

frontend/lib/types/Colors.ts

@@ -9,4 +9,5 @@ export type Color =
   | "dangerous"
   | "dangerous-dark"
   | "success"
-  | "warning";
+  | "warning"
+  | "static-white";