refactor(editor): style links with brand color and subtle underline

- Use var(--brand) instead of var(--primary) for link color (blue vs
  near-black)
- Add default underline at 40% opacity, full opacity on hover
- Remove Tailwind HTMLAttributes from Link extensions — let CSS control
  all link styling uniformly
- Mention cards unaffected (a.issue-mention overrides with color: inherit)

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

apps/web/features/editor/content-editor.css

@@ -287,14 +287,15 @@
 
 /* Links */
 .rich-text-editor a {
-  color: var(--primary);
-  text-decoration: none;
+  color: var(--brand);
+  text-decoration: underline;
+  text-decoration-color: color-mix(in srgb, var(--brand) 40%, transparent);
+  text-underline-offset: 2px;
   cursor: pointer;
 }
 
 .rich-text-editor a:hover {
-  text-decoration: underline;
-  text-underline-offset: 2px;
+  text-decoration-color: var(--brand);
 }
 
 /* Issue mention cards — inline cards that sit within text flow */

apps/web/features/editor/extensions/index.ts

@@ -27,17 +27,11 @@ const LinkEditable = Link.extend({ inclusive: false }).configure({
   openOnClick: true,
   autolink: true,
   linkOnPaste: false,
-  HTMLAttributes: {
-    class: "text-primary hover:underline cursor-pointer",
-  },
 });
 
 const LinkReadonly = Link.configure({
   openOnClick: false,
   autolink: false,
-  HTMLAttributes: {
-    class: "text-primary hover:underline cursor-pointer",
-  },
 });
 
 const ImageExtension = Image.extend({