Acknowledge all of the current user's unacknowledged mention-tasks in a project.

Sets `acknowledged: true` on every unacknowledged mention-task assigned to the authenticated user in the project. Idempotent — already-acknowledged tasks are left as-is and never re-counted. Scoped to the caller's own tasks; other users' tasks are untouched.

curl -X PUT "https://example.com/tasks/acknowledge-all/497f6eca-6276-4993-bfeb-53cbbbba6f08"

{  "acknowledged": 0,  "unacknowledgedCount": {    "total": 0,    "creator": 0,    "reviewer": 0  }}