fix: wikilink underline now follows type color

The underline was implemented via border-bottom with a hardcoded
var(--accent-blue), ignoring the per-type color set on the element.
Changed to currentColor so the underline inherits the dynamic color.
Also removed the no-op textDecorationColor inline style (text-decoration
is none; the visual underline comes from border-bottom).

Bonus: fixed pre-existing TS build error in useEditorSave.test.ts
(vi.Mock namespace → Mock type import).

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

src/theme.json

@@ -92,7 +92,7 @@
     "wikilink": {
       "color": "var(--accent-blue)",
       "textDecoration": "none",
-      "borderBottom": "1px dotted var(--accent-blue)",
+      "borderBottom": "1px dotted currentColor",
       "cursor": "pointer"
     }
   },