graphview: Use #808080 as link color

For good contrast in both dark and light mode, the link color is now a semi-light gray instead of complete black, which had bad contrast in dark mode and good constrast in light mode.

Later, we can seperate color palettes for light and dark mode, but only together with a dark mode toggle button or system-wide darkmode toggle.

src/style.css

@@ -1,7 +1,7 @@
 @define-color audio rgb(50,100,240);
 @define-color video rgb(200,200,0);
 @define-color midi rgb(200,0,50);
-@define-color graphview-link black;
+@define-color graphview-link #808080;
 @define-color graphview-grid @text_view_bg;
 
 .audio {