Two bugs were forcing the overlay back on:
1. ContentView.thinkingIndicator used `isActiveRunning || !isActiveDismissed` — the OR meant running tasks always showed the overlay regardless of user dismiss. Changed to just `!isActiveDismissed` so user controls it entirely.
2. AgentViewModel+TaskExecution and +TabTask set `thinkingDismissed = false` on EVERY iteration of the task loop. Now only set on iteration 1 — subsequent iterations respect the user's manual dismiss.

The overlay is a heads-up display, not required during a task. User can hide it and focus on activity log.