fix: recover from phantom 'running' state after crash/restart

The run-cancel registry is in-memory; a container restart mid-run leaves
accounts/tasks persisted as 'running' with no goroutine, wedging cancel
(not-in-map -> 409) and blocking remove/re-run.

- startup: ResetRunningOnStartup clears stale 'running' -> 'idle' on boot
- cancel handler: when no live goroutine, ClearStuckAccount + ReconcileTaskStatus
  reset the stuck account (and its task) instead of returning 409

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01MMHQTtnQtQqL8muAXHr9kd

cmd/server/main.go

@@ -33,6 +33,14 @@ func main() {
 		slog.Error("store", "err", err)
 		os.Exit(1)
 	}
+	// Clear phantom "running" left by a prior crash/restart — no goroutines
+	// survive a restart, so any persisted "running" is stale.
+	if t, a, err := st.ResetRunningOnStartup(context.Background()); err != nil {
+		slog.Error("reset stale running", "err", err)
+		os.Exit(1)
+	} else if t > 0 || a > 0 {
+		slog.Warn("reset stale running statuses on startup", "tasks", t, "accounts", a)
+	}
 	hub := wshub.New()
 	orch := orchestrator.New(st, hub, cfg.EncKey, cfg.WorkerConcurrency)
 	srv := httpapi.NewServer(cfg, st, orch, hub)