fix(post): link board-specific option errors to supported boards

When fortune or dice options are used on the wrong board, show which
boards support them with clickable links in the post form and reply modal.

src/components/post-form/post-form.module.css

@@ -233,6 +233,12 @@
   color: red;
 }
 
+.error a,
+.error a:visited {
+  color: inherit;
+  text-decoration: underline;
+}
+
 .formError {
   margin: 8px 0;
   padding: 6px 5px;