feat: add test-coverage-improver agentic workflow (#344)

* Initial plan

* feat: add test-coverage-improver agentic workflow

Co-authored-by: Mossaka <5447827+Mossaka@users.noreply.github.com>

* fix: add explicit bash command patterns for security

Co-authored-by: Mossaka <5447827+Mossaka@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: Mossaka <5447827+Mossaka@users.noreply.github.com>

Author: Copilot