Implement full E2E, integration, component, and unit tests, and resolve all leftover tmux-to-herdr issues in UI and core scripts

.agents/skills/multi-agent-mux-ui/apps/mam_desktop/test/widget_test.dart

@@ -15,7 +15,7 @@ void main() {
         name: 'demo-session',
         server: 'default',
         status: 'running',
-        tmuxAlive: true,
+        herdrAlive: true,
         pane: const Pane(
           pid: 123,
           cwd: '/x',
@@ -26,7 +26,7 @@ void main() {
         resumeState: 'yes',
         jobId: '-',
         jobStatus: '-',
-        attachCommand: 'tmux attach -t demo-session',
+        attachCommand: 'herdr session attach demo-session',
         driftClasses: const ['B'],
       ),
     ];