[FEATURE] Add delete_scheduled_task to the scheduled-tasks MCP (Cowork)

Summary

The Cowork scheduled-tasks MCP exposes only create_scheduled_task, list_scheduled_tasks, and update_scheduled_task. There is no delete_scheduled_task. Disabled or obsolete tasks accumulate in the list permanently and cannot be removed from inside Claude Code.

Reproduction

1. Create two tasks via create_scheduled_task (or via the Cowork UI).
2. Disable one of them by calling update_scheduled_task(taskId: "...", enabled: false).
3. Call list_scheduled_tasks — the disabled task still appears.
4. There is no MCP method to remove it.

Editing the underlying state file does not help: the MCP keeps the canonical state in memory and rewrites the file every few minutes, restoring the entries.

Tested state file (Windows):
%APPDATA%\Claude\claude-code-sessions\<accountId>\<sessionId>\scheduled-tasks.json

Observed sequence on my machine (2026-05-17):

• 11:03 — file shows 5 tasks (4 disabled, 1 active).
• 11:04 — I edited the file on disk to remove the 4 disabled entries (file shrunk to ~80 KB, 1 entry).
• 11:07 — MCP server rewrote the file (back to 232 KB, 5 entries).
• 11:08 — Disk again shows 5 tasks; list_scheduled_tasks likewise.

Impact

• Cannot maintain a clean task list. Old experiments and renamed tasks remain visible forever.
• Workaround (closing Claude Code, editing the file, reopening) is fragile and loses the active session.
• update_scheduled_task accepts no delete: true flag, so even a privileged side-channel deletion is unavailable.

Proposed fix

Add delete_scheduled_task(taskId) to the MCP:

• Removes the entry from in-memory state and from the persisted state file in the same atomic write.
• Refuses if enabled: true unless force: true is provided (safety check against accidental deletion of live schedules).
• Returns a clear result: { deleted: true, taskId } or an error if the taskId does not exist.

Environment

• Claude Code version: 2.1.138
• OS: Windows 11
• MCP server: built-in scheduled-tasks (Cowork)