Merge remote changes, standardize button text color to --text-white CSS variable

Resolved merge conflicts by keeping the CSS variable approach (var(--text-white))
instead of hardcoded #fff for button text colors across all components.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

frontend/src/index.css

@@ -44,7 +44,6 @@
   --badge-blue-text: #63b3ed;
 }
 
-  --color-default: #000000;
 /* Ensure all interactive elements show pointer cursor */
 button,
 [role="button"],

frontend/src/melodies/MelodyDetail.jsx

@@ -143,7 +143,7 @@ export default function MelodyDetail() {
             <button
               onClick={() => setShowDelete(true)}
               className="px-4 py-2 text-sm rounded-md transition-colors"
-              style={{ backgroundColor: "var(--danger)", color: "var(--text-white)" }}
+              style={{ backgroundColor: "var(--danger-btn)", color: "var(--text-white)" }}
             >
               Delete
             </button>