Apply one patch to up to 50 tasks atomically.

Same patch for every id (1–50). Admits exactly what PATCH /tasks/{id} admits: the tasks of the projects the caller may edit (a teammate's task included) and their own tasks with no project. Before any write, an id the caller cannot see is 404 not_found and a task they see but may not edit (a team viewer) is 403 forbidden — nothing written. Runs in one transaction: an id that escapes the rule in the database rolls back the whole batch (400 invalid_request, detail batch_partial_failure). The patch admits exactly the columns PATCH /tasks/{id} allows for bulk edits: title, description, status, priority, is_urgent, is_important, is_for_today, due_date, project_id ("" clears due_date / project_id). The TEMPLATE (master) of a materialized recurring series is never written by a batch — for every field of the patch (AGF-382): it is left as it is and listed under skipped (reason: "series_template", with a hint), while the other ids ARE written — never a refusal of the batch. Its occurrences are the tasks to complete, date or flag; the series changes through PATCH /tasks/{id}/recurrence/rule and moves with PATCH /tasks/{id} (project_id). MCP sibling: tasks_batch_update.