feat(task-toast): display skills and concurrency info in toast

- Add skills field to TrackedTask and LaunchInput types
- Show skills in task list message as [skill1, skill2]
- Add concurrency slot info [running/limit] in Running header
- Pass skills from sisyphus_task to toast manager (sync & background)
- Add unit tests for new toast features

src/features/background-agent/manager.ts

@@ -132,6 +132,7 @@ export class BackgroundManager {
         description: input.description,
         agent: input.agent,
         isBackground: true,
+        skills: input.skills,
       })
     }