feat(ui): show unread indicator in side panel session cards

Reuses the pulsing blue dot (.tab-unread) next to the session name in
the mobile side panel for inactive sessions with unread output.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: dorlugasigal

public/terminal.html

@@ -3554,6 +3554,7 @@ <h3>
               '<span class="side-panel-card-name">' +
               esc(ms.name) +
               '</span>' +
+              (ms.hasUnread && !isActive ? '<span class="tab-unread"></span>' : '') +
               '<span class="side-panel-card-status" style="background:' +
               safeColor(statusColor) +
               '"></span>' +