Distinguish local agent host harness in customizations view (#312064)

* Distinguish local agent host harness in customizations view

The local agent host registered its customizations harness with the bare
agent displayName ('Copilot CLI'), making it visually identical to the
extension-host Copilot CLI harness. Append '[Local]' to match the
existing convention used by workspace labels and agent session provider
names.

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

* Localize [Local] suffix in agent host harness label

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

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