feat(ui): add session directory display and improve error handling

- Show working directory in session cards with tooltip for full path
- Add toast notifications for API call failures
- Check HTTP response status before parsing JSON

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

src/web/public/styles.css

@@ -621,6 +621,19 @@ body {
   font-weight: 500;
 }
 
+.session-dir {
+  font-size: 0.65rem;
+  color: var(--text-muted);
+  font-family: 'SF Mono', Monaco, monospace;
+  background: rgba(255, 255, 255, 0.05);
+  padding: 0.125rem 0.375rem;
+  border-radius: 4px;
+  max-width: 80px;
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
 /* Session Resources Display */
 .session-resources {
   display: flex;