Fix required-task abort message and clarify template/concurrency comments

Format the required-task abort line with the standard "** 🤖" status
prefix and drop the stray Markdown italics marker so it renders like the
other status lines.

Correct the non-mapping getattr comment to state that item access is
tried before attribute access, which flips stock Jinja's order.

Correct the multi-model repeat example: the (model, item) cross product
runs under a single model_concurrency bound, not model_concurrency times
async_limit.

Skip the shell-task fan-out test on Windows, where shell tasks are
unsupported (they require a POSIX shell and a reopenable temp file).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: anticomputer