Scheduled/desktop tasks stop firing once a manual session is active

## Summary
Scheduled (desktop) tasks configured via the scheduled-tasks mechanism (cron expressions, e.g. `0 12 * * *`) stop firing autonomously once another Claude Code session is already active/open, even though the documentation states scheduled tasks should run "independent of any manual sessions you have open".

## Observed pattern
On one occasion, two scheduled tasks fired normally at their scheduled times (12:02 and 12:06) while no other session was active. From the moment a third session became active (12:12) until midnight — over 12 hours — no further scheduled task fired at all, including:
- multiple daily cron tasks
- a one-time `fireAt` task

So this affects both `cronExpression` and `fireAt` scheduled tasks, and is not limited to one specific task definition.

On a separate occasion, scheduled tasks eventually did fire, but with growing delays through the day as more sessions queued/overlapped (e.g. a task scheduled for ~12:30 actually starting at ~13:05, a task scheduled for ~12:54 actually starting at ~14:11), consistent with contention against already-active sessions rather than a hard cron miss.

## Expected behavior
Per the documentation, scheduled tasks should start at their scheduled time regardless of whether a manual session is already open, without requiring the user to close or wait out other active sessions.

## Additional note
The built-in "skipped run" reasons currently surfaced to users (computer asleep, previous run still in progress, another scheduled task running) do not include "a manual session is active" as a stated reason, even though that appears to be what is actually happening — so users have no visibility into why a task didn't fire.

## Environment
- Windows 11
- Claude Code desktop app with scheduled tasks (cron-based)

Start by reproducing the scheduled-tasks behavior with both a cronExpression and a one-time fireAt task, first without and then with a manual session active. Check the scheduling and skipped-run reporting paths for the documented missed-run conditions. Done means scheduled tasks fire on time despite an active manual session, or the user-visible reason accurately explains any skip.

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