/sw-start now auto-pauses existing in-progress workflows instead of blocking with "There is already an active workflow". The previous block behavior led to "shadow" workflows (in-progress in stelow.json but invisible to the UI/LLM because getActiveWorkflow() returns only the first) when users called /sw-start multiple times in succession.
New behavior:
0 in-progress: continue (no-op)
1 in-progress: pause it, then create new
2+ in-progress: pause all, then create new
Paused workflows stay recoverable via /sw-resume <name> and are fully removable via /sw-archive <name> or /sw-archive purge.
The user is informed via ctx.ui.notify with the names of paused workflows.