Add support for listing completed tasks

[krisrowe]

Problem

The list_tasks tool only returns incomplete tasks. There's no way to retrieve completed tasks, which are needed for:

• Reviewing recently completed work
• Finding tasks to update with resolution notes
• Auditing task history

Proposed Solution

Either:

1. Add a status parameter to list_tasks (e.g., status: "completed", status: "all")
2. Add a separate list_completed_tasks tool

TickTick has a separate API endpoint for completed tasks that should be leveraged.

[krisrowe]

API Investigation (2026-01-05):

The TickTick Open API does NOT have an endpoint for listing completed tasks.

• GET /open/v1/project/{projectId}/data explicitly returns only "Undone tasks under project"
• No sorting, pagination, or filtering parameters for completed tasks
• Individual task endpoints require knowing the task ID

Workaround options:

1. Capture task data before calling complete_task and store locally
2. Investigate unofficial/internal API used by ticktick-py
3. Periodic full sync with local delta tracking

See API docs: https://developer.ticktick.com/docs#/openapi