feat: use favicon artwork for header logo mark; ignore .vscode

Co-Authored-By: Claude Opus 5.5 (1M context) <noreply@anthropic.com>

styles/globals.scss

@@ -329,18 +329,17 @@ button {
   font-weight: 600;
 }
 
+// Same artwork as public/icon.svg; the ring keeps the dark tile visible in dark mode.
 .logo-mark {
-  display: grid;
-  place-items: center;
+  display: block;
   width: 32px;
   height: 32px;
-  border-radius: 9px;
-  background: var(--text);
-  color: var(--bg);
-  font-family: var(--font-mono);
-  font-size: 0.8125rem;
-  font-weight: 700;
-  letter-spacing: -0.02em;
+  flex-shrink: 0;
+  border-radius: 7px;
+}
+
+[data-theme='dark'] .logo-mark {
+  box-shadow: 0 0 0 1px var(--border-strong);
 }
 
 .logo-text {