Font weight tweaks (#13854)

Font weight 500 is not discernible from 400 on some fonts/operating
systems so push them back to previous value 600 except for
fomantic-ui elements which stay at 500.

Co-authored-by: techknowlogick <techknowlogick@gitea.io>
Co-authored-by: 6543 <6543@obermui.de>

web_src/less/_user.less

@@ -9,7 +9,7 @@
       }
 
       .header {
-        font-weight: 500;
+        font-weight: 600;
         font-size: 1.3rem;
         margin-top: -.2rem;
         line-height: 1.3rem;