Add kanban_bulk_create_tasks tool for batch task creation

[rephapeng]

Summary

Adds a kanban_bulk_create_tasks tool to the kanban skill so an agent can create several board tasks in a single call, instead of issuing one kanban_create_task call per task.

Why

When asked to create several tasks at once (e.g. a multi-step plan like 9B/9C/9D), the model naturally reaches for a single "bulk create" call. Since no such tool existed, it would hallucinate a kanban_bulk_create_tasks call. The quality monitor then rejected the unknown tool, and after the 2-correction cap the model frequently gave up and falsely reported a "board/registry error server-side" — so the tasks were never created at all.

Providing the real tool removes that failure at the source: the call the model already wants to make now exists and succeeds.

What it does

• skills/kanban/backend/tools/kanban_bulk_create_tasks.py — wraps kanban_create_task.execute once per item, so permission checks, validation, and single-task dependency handling stay byte-for-byte identical to the single-create path. The sibling tool is loaded by file path because skills/ is not an importable package.
• skills/kanban/tools.json — registers the tool schema so it's exposed to the agent.

Behaviour

• Accepts a tasks array (max 50 per call). Each item takes the same fields as kanban_create_task (title required; description, priority, assignee, dependencies optional).
• Partial-on-error: a failure on one task does not abort the rest. Returns {status, created_count, task_ids, results, errors} where status is:
  • success — all created
  • partial — some failed
  • error — all failed
• Intra-batch dependencies via depends_on_index (1-based index of an earlier task in the same batch). The referenced task's real id is resolved once it is created, so e.g. 9C/9D can depend on 9B without knowing its id in advance.

Testing

• python -c "import ast; ast.parse(...)" — tool module parses
• json.load(...) on skills/kanban/tools.json — schema is valid JSON