fix(ui): improve monitor panel icons and width

- Change toggle icon to show ▲ when closed, ▼ when open
- Update detach/attach icons: ⧉ (detach) and ⊞ (attach)
- Adjust panel width to 380px

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/web/public/app.js

@@ -1797,7 +1797,7 @@ class ClaudemanApp {
       panel.style.width = '';
       panel.style.height = '';
       if (detachBtn) {
-        detachBtn.innerHTML = '↗'; // Detach icon
+        detachBtn.innerHTML = '⧉'; // Detach icon (two overlapping squares)
         detachBtn.title = 'Detach panel';
       }
     } else {
@@ -1805,7 +1805,7 @@ class ClaudemanApp {
       panel.classList.add('detached');
       panel.classList.add('open'); // Ensure it's visible
       if (detachBtn) {
-        detachBtn.innerHTML = '↙'; // Attach icon
+        detachBtn.innerHTML = '⊞'; // Attach icon (squared plus - dock back)
         detachBtn.title = 'Attach panel';
       }
       // Setup drag functionality