fix(worker): allow the done toggle from any non-Running status

MarkDoneAsync was Idle-only, so a finished task (typically a list-handler
run with no worktree to merge) could not be ticked off. Guard on Running
instead and cover the other statuses with tests.

src/ClaudeDo.Worker/CLAUDE.md

@@ -70,7 +70,7 @@ not conflated.
 Allowed transitions (enforced by `TaskStateService`):
 
 ```
-Idle               → Queued | Running (RunNow) | Done (manual toggle) | Cancelled (external update_task_status only, allowFromIdle: true)
+Idle               → Queued | Running (RunNow) | Cancelled (external update_task_status only, allowFromIdle: true)
 Queued             → Running | Cancelled | Idle | Failed (OverrideSlotService preflight gap)
 Running            → WaitingForReview (standalone success, no children)
                    | WaitingForChildren (parent with pending children)
@@ -80,8 +80,14 @@ WaitingForReview   → Done (approve) | Queued (reject-rerun, +feedback) | Idle
 Done               → Idle (re-run)
 Failed             → Idle | Queued
 Cancelled          → Idle | Queued
+
+any except Running → Done (manual done toggle, SetTaskDone)
 ```
 
+The manual done toggle is the one cross-cutting transition — it ticks a task off from **any**
+status except `Running`, skipping the merge on purpose (a worktree-less list-handler task has
+nothing to merge; a worktree task's branch just stays Active for the worktrees overview).
+
 **Unified parent model.** Every parent — planning *or* improvement — flows
 `… → WaitingForChildren → WaitingForReview → Done` via the single `TryAdvanceParentAsync`.
 Planning/improvement **children** go straight to `Done`; only the parent is reviewed.