Reject a Dash-Prefixed Agents Name Before the Handoff to Install-Agents #3129

bootstrap.ps1 forwards each -Agents name to install-agents.ps1 through pwsh -File, which binds any argument starting with - as a parameter name, case-insensitively. bootstrap.ps1 -Agents '-All' (or '-a') therefore binds the -All switch and installs every tool, and the unknown-option check in install-agents.ps1 never sees it because the argument was bound rather than left over.

On Linux, bootstrap.sh --agents --all passes --all to install-agents.sh the same way, and its option match is -a | --all.

Fix on both sides by rejecting any -Agents/--agents name that starts with - in the bootstrap loader before the handoff, and pin it with a test on each. Found by the local review pass on the branch answering #3065, where it pre-exists on develop.