Summary

Adds nc_calendar_complete_todo — a one-shot "complete this task" tool that wraps the existing update_todo to set STATUS=COMPLETED, PERCENT-COMPLETE=100, and a COMPLETED timestamp in a single call.

Why

The same operation is already possible through nc_calendar_update_todo:

update_todo(
  calendar_name=..., todo_uid=...,
  status="COMPLETED",
  percent_complete=100,
  completed="<now in ISO 8601>",
)

…but for AI clients, "complete this task" is a much more natural phrasing than "set three specific fields, and remember to compute the current timestamp." The dedicated tool also pairs naturally with the existing create_todo / update_todo / delete_todo trio, mirroring CalDAV libraries that ship a one-shot complete operation (e.g., the Node CalDAV client stack).

The new tool is a thin wrapper:

async def nc_calendar_complete_todo(calendar_name, todo_uid, ctx, completed_at=None):
    if completed_at is None:
        completed_at = dt.datetime.now(dt.timezone.utc).isoformat()
    return await client.calendar.update_todo(calendar_name, todo_uid, {
        "status": "COMPLETED",
        "percent_complete": 100,
        "completed": completed_at,
    })

No client-side, model, or schema changes — the existing update_todo client method already accepts these three fields.

Verification

End-to-end against a live Nextcloud 33.0.2 instance:

1. nc_calendar_create_todo(calendar_name="tasks", summary="…", description="…") → returned UID
2. nc_calendar_complete_todo(calendar_name="tasks", todo_uid=<UID>) → {"status_code": 200, "uid": "<UID>", "href": "…"}
3. nc_calendar_search_todos(calendar_name="tasks", query="…") → entry shows status: "COMPLETED", percent_complete: 100, completed: "2026-…"
4. nc_calendar_delete_todo(...) cleanup OK

Notes

• Annotation: idempotentHint=True — calling complete on an already-completed todo just refreshes the COMPLETED timestamp (matches CalDAV semantics).
• Scope: todo.write, calendar.read (same as update_todo).
• License: AGPL-3.0, same as the project.